Having played the game a few weeks ago...
Things I like:
- SEVERE damage scaling. Starting your combo with a light attack almost guarantees your overall combo damage is going to suck, and damage is already pretty low overall.
- Normals that were cancellable in 2D are now cancellable in 3D - meaning you can completely ignore the SAs if you want.
- Jump attacks feel a little more "correct." You can actually crossup with some of them now like you could in 2D (like Terry's jump D).
- Limits on OTG and wallbounce hits. You can only juggle/OTG the opponent a fixed number of times before they recover.
- Very complete and varied movelists. Just about everyone has full movelists and at least 2 DMs. A lot of characters like Kyo and Iori have also gotten new moves that weren't ever seen in 2D.
- Graphics are improved in a lot of subtle ways. Hair/cloth physics, changing facial expressions (even during fights) and some nice lighting in the stages.
- The game just has a lot more personality than MI1. Lots more character interaction, lots of cameos, and stuff like the extra missions and unlockable classic Neo Geo music. Some of the alternate outfits really crack me up too, like "Terry Badguy." lol.
What I don't really like:
- The game still goes too fast, IMO. Because of the speed of the game, it's still kind of easy to spaz on buttons and hope you hit something.
- Rolls are still relatively useless beyond avoiding fireballs. There still seems to be that 2K3-style lag on start and finish...
- The parry feature is OK, but I still think the risk/reward ratio on that thing is a little skewed. And being able to parry back and forth repeatedly isn't my idea of fun. If you were predictable enough for me to be able to parry your attack successfully, I want to be able to smack you one, not have my attempted counterattack smacked away by a counter-parry.
- Unlockable characters in some cases have most of the stylish arts of their "cloned" characters. In some cases it makes sense, and most of the time there are significant changes, but then you have characters like Hanzo who has almost nothing to differentiate him from Nagase. Or Lilly who has maybe two moves different from Billy. Uh...
Overall, I think it's a significant improvement over MI2, although there are still a number of notable rough spots. It probably has more replay value than the former game though, since the system is more solid.