GBA is more comparable to SNES. It's a neat little box. It's not overally powerful, but just try playing some GBA games on full screen and you'll see how good they can be.. It's early days and everything is still first generation. You pnly have to check out Ecks vs Sever to see a Doom beater... Mario Kart Advance, well you must have seen that on TV, it's closer to the N64 version than SNES..
It's not as powerful as a Saturn.. There's no real processing power for 3D, but all the same it does a good job.. Just wait for games like Tekken and Virtua Fighter to show what can be done, with some clever graphic tricks.
There are some exciting developments in GBA emulation. It already does a pretty good job of running emus of Sinclair Spectrum, Space Invaders Arcade Machine and Most notably NES. I also have it from people very active on the GBA Emu scene that shortly, a Sega Master System / Sega Game Gear emulator for GBA will be released.. The code is near complete, with some optimisation left to do.. Apparantly it runs at full speed. My source is a trustworthy one and is well respected on the GBA scene by users and programmers alike..
It may not have the classics like Panzer Dragoon, but with SEGA now developing for GBA, you never know what they'll squeeze out of the wee beastie.