I know that they changed Streets of Rage 3 a bit... they had gay guys that you had to fight, and they took them out of the game all together. Also, those stupid English voices were not in the JPN version of the same game.
Other than that, I don't know about any differences in the first two. Who cares, SOR2 is the best of them all anyhow.
Actually I like SOR1 the best. Probably because it holds the most memories for me. Plus I loved how no matter where you were you could always call in you own special squad car to bazooka the enemy...
You could find the best special weapon in a video game EVAR!! PEPPER!
Toss some of this stuff and watch the bad guys go into a sneezing fit
After SOR1 Adam never recovered and he was my fav, instead we got skate and Max.
I really like 3 because of the special trick to play Shiva and the kangaroo.
You can play megadrive games on just about any megadrive/genesis as far as I know. I have a version 1 Japanese megadrive that plays European and American megadrive games and a genesis module for my pioneer laseractive that also plays just about anything related to the megadrive. Some of the newer games might have some compatibility problems and all mega cd/sega cd games have teritorial lockouts. :P