I also played game day today. I agree that the monsters were damn strong.
Granted, some of it was due to people looking up new rules, but combat rounds took longer than they do in my current 8th level 3.5 game. And even if they do streamline over time (as folks become used to the rules), there are simply more rounds to be gotten through, because the monsters have so many more HP's.
I really dislike that they got rid of touch AC's.
I prefer Tome of Battle Crusader healing than the healing surges. Everyone in our party had used their healing surges, 3 of the 5 of us were down to under 5 HP's, and the cleric had used up all his per encounter healing surge "spells." And none of the monsters were even bloodied yet, aside from the main BBEG, who was unconcious, but then got a 20 on his save...
The attacking of different "AC's" for your "saves" causes more problems than it solves. Every time the DM would attack, and then we'd have to ask what AC he was trying to hit, he'd have to stop, look it up...
And with the save-attacking AoE spells, the DM has to sit there rolling 3 or 4 times, attacking against each PC. Asking for "Fort saves!" is faster, when each person attacked is responsible for one roll. Though, I suppose the inverse happens in 3rd ed, when the PC's target multiple foes in a fireball. But now in 4th, it just means the player is rolling all the "saves," in addition to rolling and adding up damage. It's no faster on one side (and actually slower, since you're lumping all the attack saves and damage on the one player's shoulders), and slower now on the other side. Not a benefit, if you ask me, as the goal was to speed things up.
My opinion, there might be a few small ideas I'll implement in 3rd ed games, but I'm not that impressed.