I have an SP, but to be honest, I rarely ever use it. I'm not quite sure exactly what it is, but the screen on it is most definitely not backlit, and it looks pretty crappy compared to the DS or Micro screen. If you already have a DS and/or Micro (which I'm assuming you don't, since you're asking about games), you will definitely notice a major drop in picture quality if you switch to an SP. On the other hand, if you haven't played a GBA game on either of those, the SP looks pretty good.
Either way, if you're going for a good-looking screen, get a DS or Micro. If you can't afford those or you don't care too much about how the screen looks, go ahead and get an SP.
In terms of games, I really enjoy the following:
- Kingdom Hearts: Chains Of Memories (Not Reccommended If You Haven't Beaten Kingdom Hearts.)
- Mario & Luigi: Superstar Saga
- Pokemon Ruby/Sapphire/Emerald (That is, if you aren't tired of Pokemon yet.
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- Sigma Star Saga (Very, very interesting take on two tired and completely different genres.)
There are countless other awesome GBA games, those just happen to be the ones I see on my shelf that I'm really enjoying playing right now.
- CFB