Lucky for you there are are some good Castlevania games on the GBA, these are 'Castlevania: Circle of the Moon' and 'Castlevania: Double Pack'. Castlevania: Double Pack contains 'Castlevania: Aria of Sorrow' and 'Castlevania: Harmony of Dissoance' so I would specially recommend picking that one up.Originally Posted by martini178
As for Sonic games the only one I would recommend getting is Sonic Advance 2. Don't get any other Sonic games as they're not very good (with the exception of Sonic Advance one which is OK).
Two side scrolling games also worth getting are 'Metroid Fusion' and 'Metroid Zero Mission'. Both are very good so I reccomend you get them both.
4 more excellent side scrolling games are; Mario Advance 1, 2, 3 and 4. All four of these games are ports of the SNES Mario games ( Super Mario Advance 1= Super Mario Bros 2, Super Mario Advance 2= Super Mario World, Super Mario Advance 3= Yoshi's Island and Super Mario Advance 4= Super Mario Bros 3) so if don't own the SNES versions then all 4 of these are worth getting.
The 3 Donkey Kong Country games have also been ported onto the GBA, so if you don't own the SNES versions then all three of these are worth getting.
Don't worry though, not all side scrolling GBA games are ports of SNES games. Heres some good side scrollers which AREN'T ports (yes they do excist ):
Astro Boy Omega Factor
Gunstar Future Heros (I THINK this is a side scroller)
Wario Land 4 (excellent game)
Mario & Donkey Kong (very good)
Of course side scrollers aren't the only good games on the GBA. Here is a list of good non-sidescroller games on the GBA:
Advance Wars Black Hole Rising
Final Fantasy IV Advance
Final Fantasy Tactics Advance
Fire Emblem Sacred Stones
Mario & Luigi: Super Star Saga
The Legend of Zelda: A Link to The Past/ Four Swords (port of SNES version)
The Legend of Zelda: The Minish Cap
Pokemon Ruby/ Sapphire
Mario Kart Super Circuit
Pokemon Leaf Green/ Fire Red
Out of all the games I've mentioned just get the ones that sound good to you .