I've been playing several games for some time now:
Labyrinth - a really good little "roll the ball through the maze" game that has some really great ball physics and movement precision. It's $7 which may seem too much for a simple game like that, but there are 500 levels available, and really, it's as close as you can get to a real game of this kind - it's just that well simulated. The game runs at 60FPS which gives it that much more realistic feel.
Zen Pinball - Framerate seems to be locked to 20FPS which is really disappointing for a pinball game. It just feels choppy and shatters the illusion of having real ball rolling there. It's that much worse considering that the actual ball physics seem really good, and the table design is interesting.
Trism - quite addictive and very nice overall. Fun to control too.
Super Monkey Ball - The best graphics and presentation of all the Iphone games so far, and to be honest I don't think the controls are as tough as some made them be, but they are not a walk in the park either. I have been able to finish all the ten easy levels without failing once on my first attempt - but I missed many bananas. Maybe all the 'training' I had with games played with Sixaxis made this easier than it is for some people, I don't know.
Still, I'm not sure how the progression in this game works exactly. I have the crown (means I collected all the bananas) on 8 levels, and some bananas still missing on two levels. What I don't get is how exactly is this crown on a level earned? It seems like as soon as you die once on any given level, you have no chance of earning the crown there, unless you start the game from the very beginning? Is it really possible that it's this dumb? I don't see any way how to jump right into a level, it always has to go from the beginning, and it sucks playing all the way up to level 9, collecting some bananas there, then dying, and then when you respawn on that level, collect the remaining bananas and finish the level - you don't get the crown. Do I even have to collect these crowns or should I just keep playing on Hard levels (which are all completely different from the easy ones)