Powers Are Really Different
I love power cards, that is a great innovation. We've used something like that in 3.5 and it means my frustrations with characters not knowing their spells (I even ended up making a spellbook for one player!) are potentially over. Only one player chose not to use the cards and it slowed down their gameplay considerably. But the other thing about powers is that this is a completely different way of doing things. Powers interact (marking) and allow some pretty cool maneuvers. Powers also gives the players a nice way to make their characters unique, so big thumbs up. The only reservation I have is that now every character plays the same - they all have powers. This makes wizards more useful, although with a low BAB they are still quite useless in combat once their auto-damage spells (flaming sphere is quite nice in this edition) are used up.
Movement and Freaking Squares
Ok so I'm still not sold on diagonals counting the same as straight movements, I'll live. But now all the effects are squares?
Wizard "Watch me cast a fire cube!"
Fighter "A what?"
Wizard "A firecube, you know to avoid pesky pixelation."
Rogue "My mother was killed by damn pixies!"
Frustrated Wizard "No! Pixelation. It is when..."
Party is eaten by monsters annoyed by their debate.
Remember THAC0? What a great innovation. Then D20 made things even more simple by making all the math move in the same direction! Yay! In every version it takes a while to get used to the math. Last night we discovered the addition of variables. Now weapons do damage based on interesting algebra: 2(W)+STR+WIS = ???? It is actually quite elegant when you get your head around it. But there are a lot of fun little numbers to calculate - best to do these before hand. Passive checks (nice!), Surge values (Surges are actually quite interesting. We had some fun with those in the first encounters!), attack bonus', etc. What I would say is that this is quite doable, once you have your head around the crunch of the system you are golden. Now what was W again?
Got Rid of Skill Creep
The last one I'll look at is a big Kudo. They got rid of skill creep. By combining skills into categories (and killed the ability to max these out) skill become a lot more playable. DCs are simplified as well, based on the tier you are playing at you have a baseline DC value that you can fudge around. As a DM it is nice to have a baseline.
I had a lot of fun DMing the new version. I think it is quite playable. I ditched a few things - milestones? meh. I'd rather award things like that in a more arbitrary fashion. The scenario we are running does have a boss on each level so that warrants an Action Point. I'll have to give milestones some more thought later. BTW for the DMs out there, nothing beats a creepy tapestry to cause the players to waste an hour in an empty room.