Due to adaptions related to visability problems GBA games' graphics tend to look a bit pale and washed out when emulated.
Though not built for the purpose the GBA doesn't do too bad a job rendering polygons, better than the SNES anyway, which it often compared to in regards to hardware potential (for no great reason, really, apart from some library crossover).
Here's a list of games which use polygons in some way:
And here's a list for engines, tech demos, homebrew, etc.
Game which use a variety of techniques to appear 3-D, appearing similar to raycasting.
Some advice for EZ-Flash IV users.