I got into the beta on Sunday and so far I've already beaten the beta with all the characters. It only takes a little over 2 hours for each one. The beta is very easy, I never died, nor did I need to use a single pot. Then again I never died in the first half of act 1 in diablo 2 either.
I do like how the spell damage of the spell casting classes (well all classes actually) is tied to your weapon. It makes finding good weapons for your casters just as important as your other classes. I do wish in the tooltips it would tell you your skills damage potential instead of just telling you what % of your base damage it did. I also like how all spells/skills can crit.
The skill system and leveling up is a little different. I miss alocating points in my stats (makes you feel like your customizing your char), however I don't miss having to worry about if I'll be able to equip some piece of armor later on b/c I didn't put any points into strength. I also miss allocating points into skills (again for customizing reasons), but on the flip side its very nice to be able to change to a different skill set to try things out and not have to worry about weither you permanately screwed up your char. It'll be nice to see how runes and gems work out, since it should alleviate my "customization" concers.
The limit on equipable skills is pretty well limiting, especially in the beta since you can only get 4 equipable skills at lvl 12, and until you unlock the third slot at lvl 6, your char seems a little gimped. You can also get a max of 3 passive selected skills (only 1 in beta), although from the looks of it, you can't attach a rune to passives, which would be dissapointing. In addition your "aura" or armor spells have to be recast every 30,60, or 120 seconds (depending on the spell), which is very annoying. They already take up one of your precious few skill slots, why they can't make it a permanent effect is kinda of silly.