Diablo 3 will never live up to the other games in the series, both prior games were amazing, but D3 can certainly still make a name for itself. Once you get past the horrible story, voice acting, and hand fed plot: the core game is pretty solid til you hit inferno. Inferno was a lazy attempt to challenge players/fans, and a poor end game solution to which even Blizzard admits to now. Knowing Blizzard North, the team responsible for the success of this series is no longer with the company, but left them there unfinished work of Diablo 3, a pretty solid game formula, and past game to see how the game should work; Blizzard was handed a successful game on a silver platter, and still manage to mess it all up. The system and changes they have made to the game prevent them making the game more like diablo 2 with out making people angry, but leaving things in the state is now is making people angry already. They are loosing players and they need to do something, and quick.
I am going to throw out what I think blizzard did wrong, some suggestions how to correct their mistakes. Feel free to comment or add to what I have to say, you do not have to agree with what I am saying, as this is just my opinion. And in advance sorry for any grammar.
1) Items - This has always been the backbone of the diablo series. Items we have now are very generic and boring, the unique/legendary items are very underpowered, and many items are polluted with useless stats. Items missing stat like Vitality and All resist for most class making the items almost useless, and the items with these stats are all overpriced in the AH. Now that people has invested not only time but money, changing items could get harry. How ever they need to get rid of useless stats, or at least lower the amount of useless stats we have. Legendary items need special effects to make them wanted by players ( not every item, but enough to make some items worth finding.) Depending on how they change items, they should refund or credit players gold/money for what they spent on what they are currently using; but I would not hold my breath on this.
2) Group games - Currently there is more reason not to play in a group than there is to play in one. Between the increase of difficulty with out the increase of reward and the horrible magic find system, more people rather play solo. This is less fun and not the way diablo should be played. The amount of experience and drop rates should increase with the additional players, also any single player should be able to easily kill a pack of mobs on there own. People with high MF should not be punished because the other players do not have as much, everyone should either get the highest amount of MF among the players, or everyone should have their own, Making people wanting to play in group will improve the game play greatly, and hopefully rise it out of the stagnant water diablo it is currently in.
3) PVP - This is something that should of been in the game at launch or released very soon after. The old system was very basic, and they could improve on it a lot. What i am about to suggest could be another idea that might look good on paper, but in actual play not work so well. Arenas are a no brainer, but there should be other mods like capture the flag, king of the hill, and open world pvp. Providing other way will spice things up, and offer more to the player. There should also be a rating system attached to the PVP, so it can match you up against people with in the same range of skill/play-style. This also could offer some type of ladder ranking they can put up, and reset every so often.
4) Secrete Cow level? - Whimsey shire in my opinion was a slap to the diablo fans' faces. This cartoon world was developed off of the earlier complaints about the games art directions, The shirt was funny, this secrete level was sad. To get to this level also took to much time, gold, and luck to be able to enter. Even though many players have played through it once already, they could of delivered better and more. We should of had multiple secrete levels to get into and find, where the challenge was with in this level and not trying get into it, they should also be tied with in some part of the story and lore. Maybe something like entering the thieves' guild, and having to fight the leader of the group.
5) Classes - We should have enter Diablo 3 with as many choices of heroes to play as we had with Diablo 2. Having less choices is boring, Having at least 7 classes to choose from the beginning would of also helped the games progression. Not only are we lacking the variety of classes, they feel less powerful than the D2 classes. The classes feel limited, and there honestly is not a character for everyone. I should not have to run and kite every group of champions in the game, most of them should be easily beatable, we all want to feel like a god. Basic stats on every character should be rose higher, there should be quest we can do to improve our character the first time we beet it per difficulty (give us addition life, resist, ect...)
6) End Game - this is a huge topic as more people reach inferno and realize blizzards mistakes. Inferno should never been the end game, but rather 1 place people could farm gear, it should of had a static challenge amongst all the acts that was slightly harder than Hell act 4, and higher drop rates - we should never had a place in diablo that was a gear check and that was a wipe fest. They should of had more things to do beside MF and PVP since they removed the old trading system. Other game mods like a survival game where you try to live the longest in a game of endless wave of enemies, and the people with the highest score get mentioned on some ladder. Games mods like this, PVP, and special events should be the things that drive people to get the better gear, not trying to progress through the game a fourth time.
7)Nephalem Valor buff - this sounded way better when they described it, and once you seen it in practice not that big of deal. IF this was not limited to 5 stacks and you could start at the beginning of the act and finish it with something like 20+ stacks of the buff would of been better. This could allow you to remove the MF from gears completely, providing more space for better stats on the gear. It should still have the reset between acts and skill switched so it can not be too insane. As MF only can improve the rarity of the items dropped, and not the quality of the item itself - this would prevent this from being over abused.
8) charms - this was a great system and should of been included with the talisman system blizzard talked about. The stats from these gems could provide the extra stats players or lacking, or provide the stat the player needs most for there build. I understand them not wanting to have these items pollute our inventory, but dropping them completely we not necessary. Loosing the scrolls/tombs of town portal and identify was amazing ( although I wish is was faster to ID items, maybe even instant speed.)I know as a player I miss the charms.
9) Followers - here is another reason that pushes you toward single play only. You get amazing gear on your merc that you can only play with when you play by yourself? Followers could of done much better, they could of done more damage, provided better support, and different style of aggression setting (aggressive, protective, and passive,) nothing is more annoying than your follower attacking a treasure goblin before your ready for him. You should be able to bring this character in to a public game. If there is worry that there would be to much effects on the screen at once, a player could turn off or tune done the special effect of their and their teammates mercs.
10) Builds - not all builds should be end game viable, but more build should be more creative and viable at the same time. I know the skill system in Diablo 2 was not the best, but it was good enough to use in WoW before they watered it down, then imported an even more watered down skill tree. The rune system could have done more, there should not be a rune that never get used. They should all have uses, even hidden synergies with other skill, when the right skills are being used together, watch out god like fun. What they have going on right now has a good feel game play wise, but could of been better. Perhaps if they allowed Beta testing sooner, allowed more people to play it, and allowed use to play higher than level 13; a lot of this issue would have been fixed prior to launch.
11) Achievement system - if you are going to include something like this, you should offer better motivation then points which do nothing and banner modifiers. The banner things are neat but should only scratch the surface of what you could do. Maybe through various methods you could unlock special dies, or something to allow you to change the skin of an item, or some other visual reward that you can show off like your character glows. Something that can give a player braging right, however nothing should give a player advantages in the game.
12) Gold and Item sink - these are important to keep a stable economy. They should also provide a way which a players could have fun. Current systems lack this. The artisans are not that great. The jeweler and the blacksmith are both watered down versions of the horodric cube, that cost gold on top of it all. They should not cost much gold as they do, and should also allow you to gain experience through crafting items with them. Leveling them up through gold it not so much fun. Crafting should be exciting and not so under powered. Some of the best items in the game should come from the crafting items, but they are mediocre at best. Combining gems should not be so expensive either, rather the drop rate for the higher gems should be lowered, and you should have to find your way to the better gems. WE should of had the third artisan, a way to add sockets to items, and a way to enhance our items. A lot of people like the gambling in Diablo 2 and the artisans do not fill that roll exactly, as you had the chance to even gamble for a unique or set item. IF they improved these systems, and introduced other ways to spend gold/items it could keep the economy balanced. How ever Repair cost should also not cost more that what you make. This also prevents you from being able to keep playing and pushing through harder content.