well I do agree that some PSP games are more suited to playing on the go than others.
For instance, I tend to avoid playing Metal Gear on the go, because if I"m out in the daytime, it's sometimes VERY hard to see, being a pretty dark colored game. As well, I know I can't just breeze thru a mission in minutes, so dont want to get too tied up if I can only play for short blasts. The turn based nature of the game alleviates this somewhat, as it's easy to put into sleep mode in between turns... as long as you're not in the middle of a hectic fight (I use the term 'hectic' loosely).
Now Ridge Racer... aw man forget it. If I try to play this while walking around or in my wifes car while she drives, man I can't play the game for crap. It's kinda hard to be precise in these conditions, and many races/tracks become kinda difficult if trying to play them on the move. Also, sleep mode is almost useless in a game like this... as well as even pausing. Coming back to a race halfway thru, for me, usually leads to disaster... and god forbid I have to pause it while I'm in the middle of a turn/drift. I can still play the game on the go, and do well I suppose (it's not a difficult game, anyways)... but I tend not to want to bother.
Rengoku is a fast action game in 3d, and actually I do like to play this one on the go as it's very easy to play in short blasts and it has an auto lock on feature when fighting so precision is not a factor... if my wife hits a pothole it wont mess up my game. I'd say this game, with the ability to save at any time, and it's very solitary fights (you fight on a room by room basis), is very well suited for on the go play.
Golf, Lumines, Puzzle Bobble, Chaos Tower, and Dynasty Warriors, all work well on the go... of course, this gives mattmagoos argument more steam as 3 out of 5 of those are 2d games
Really though it seems to me that 2d or 3d really has very little to do with how accessible a game is as a portable, rather, it really just comes down to the style of game. For instance, Golf is in 3d, yet really, the gameplay mechanics of it echo many 2d golf games before it... it just looks nicer. Rengoku is in 3d but is a more simplistic game than say, GTA. But there will be some games for PSP that will definatley be pretty deep and probably not well suited for 5 minute blasts or playing will moving around, I can agree to that.
