The N-Gage has thousands of great games! I bought an N-Gage about a month ago at a Gamestop. The clerk asked me why I would want an N-Gage, and I told him that I just wanted something very small that could play Gameboy games. Everybody always brings their keys, wallet, and phone with them... but you rarely have the extra room for a GBA SP, let alone a DS or PSP. Of course, the clerk acted like I was an idiot. Apparently he buys into all of the latest hype, but doesn't actually know what he is selling. The N-Gage can even play ripped music CDs and ripped DVD movies!

But yeah, the N-Gage plays Gameboy, Super Gameboy, and Gameboy Color games, but not Gameboy Advance games. It can also play NES and SNES games too, though the SNES games run really slow, but fast enough for slower paced games such as RPGs (Final Fantasy, Chrono Trigger, etc). The best set of emulators for the N-Gage are here:
http://www.vampent.com/emu.htm

I highly recommend the vBoy emulator, as it is only $10 USA dollars, and it runs every GB, SGB, and GBC game at full speed and resolution. The NES and SNES emulators have to scale down the screen to get it to fit on the N-Gage's smaller screen, which can make some game text hard to read. Anyway, with vBoy and a large MMC flash card loaded with Gameboy games, you are well prepared for those boring situtations you sometimes find yourself in... when you only have your keys, wallet, and phone.

Oh and in that situation, just imagine what you would do if you were a PSP owner. Answer: day dream about playing your PSP, which you left at home because it was just too big to take along with your keys, wallet, and phone