My Pocket is arriving tomorrow! Super excited. Only have the Burai Fighter cartridge for now but will get a bunch during the weekend.
Any Advance games that are more under the radar that I should look for?
Specifically GBA? If you want to get boxed copies I'd recommend going for the Japanese ones as the packaging is far nicer.
The Bit Generations series is really interesting and somewhat obscure - seven barebones experimental games by Nintendo. Very nice tiny boxes too. Then there's Mawaru Made in Wario (Wario Ware Twisted?) which is just excellent - although the 'open' slot design and general bulk of the Pocket slightly deadens the feedback from the motion-sensing cartrtidge.
Kur Kuru Kururin was a brilliant launch title that's still worth playing. Hard as nails, I can't get anywhere near my old high scores now.
If I could only pick one GBA game though it would be Rhythm Tengoku. The last GBA game they made, never released outside of Japan but it's much better than the DS / 3DS / Wii Rhythm Heaven titles that got international releases.