The only real issue with SA2 in the latest versions is that when you press the buttons you specified for forward and back (to move your character forwards or backwards), it will tilt the character a bit to the left. It's as if you had your analog stick held slightly offcenter. Pretty obnoxious too. You can fix it by using an older build, but that would mean less compatibility. It doesn't do this in all games either for some reason... You MIGHT be able to fix it somehow by messing with gamepad calibration or something.
For those having issues with that game in nulldc, i'd recommend playing the Gamecube version in Dolphin. It's an identical game, with a few new bonuses such as pretty expansive multiplayer. At this point, Dolphin plays the game 99% flawlessly for me, much more so than nulldc. It doesn't require too beefy of a PC either, more than dreamcast, but if you have a decent dual core over 2.5ghz and a competent GPU, you'll probably be ok. I can play it fullspeed all the time on these specs-
Athlon II x2 250 @3ghz
2GB DDR2 ram
Radeon 4350 (dxdiag says it has 1274MB video memory, not sure if that's accurate, but this is a weak gpu)