My impressions are that the monk and witch doctor were strongest. They both had nice life leech skills and good survivability that out classed the other's lower survivability. The three other classes did have higher burst DPS like archon and bezerker's wrath and shadow power.
None of those build are exactly correct. Barbarian is the closest, kind of, but he had Crimson Hammer of the Ancients instead of that Weapon Throw thingy. There's quite a lot of discussion about the builds on other parts of the forums as well, go and look if you're interested.
A level 1 signature spell in a 4 VS 4 arena, it looks like a skillslot wasted. It isn't doing any damage at all...
In a classic skill tree system that would probably be true. However in D3 every skill has its place in your arsenal and the level at which you unlock it is almost irrelevant. Generally, the more simpler spells are unlocked first, but that doesn't mean that they aren't useful in the end-game. For example, except for Magic Missile's Seeker effect the Wizard doesn't have a cheap way to harass enemies from behind the safety of an obstacle.
this skill hit really hard, anywhere from 1k-2600 on crit. Its slow casting speed and finicky targeting made it a very deadly skill but difficult to use. There were many a time where I thought I was going to escape by the hair on my chin, only to be sniped for the last 2000 of my health all the way across the map.
That damage isn't bad at all from skill that costs no AP.
On top of that, based on Chaboi's report, in the PvP demo characters were mostly sporting magic or similar quality items. Meteor looks more and more like a one-shot skill for a well equipped Wizard.
I looked at the "crazy builds" video very closely, and the petless WD could crit for 17k+ damage with Fire Bomb, a skill that only deals 130% weapon damage (based on the current calculator, which may be out of date). Now think what a Wizard will be able to do.
EDIT: Actually, a Wizard will be able to crit for over 42k damage with Wave of Force (most likely with Forceful Wave) and deal 35k+ crit damage with Explosive Blast (Short Fuse). GL HF.