The mainline Mega Man series found itself mostly exclusive to Nintendo platforms up until the Sega Saturn and Sony PlayStation era, where Mega Man 8 and X4 passed over to systems not produced by Nintendo. Before then, there was only three ways to play Mega Man on a SEGA system: Wily Wars, the U.S.-only Mega Man for Game Gear, and this little unlicensed hack, Rockman X3 for Genesis.
Pinching graphics, music, and a meager handful of sound effects from Mega Man X3, you'd be forgiven at a glance for thinking this port is incredibly faithful, but it isn't. As much as I do admire the vibrancy of the stolen Super Nintendo art and the pleasant border that changes according to the stage you're on, the graphics actually break up pretty badly when the game is in motion.
As for the music, that's a real wasted opportunity. Mega Man X3 songs could potentially sound great being played through the Genesis sound chip, but these renditions aren't anywhere near pleasant to listen to at all. I do not remember enough of Mega Man X3 to tell you if these are the actual songs used in the game, but they may not be. Two versions of this ROM exist online, which are both the same besides the music.
As for the port itself, all of the mechanics of the game are in. The dashing, the upwards boost, the charged shot and the wall-kicking. These functions are all rigid. Well, more rigid than normal. The screen transitions are present but don't function very well, leading to incorrectly looped backgrounds and screen transitions that lead to empty rooms you cannot escape from.
Rooms where cutscenes would have originally occurred in Mega Man X3 are now completely empty or contain a small mini-boss encounter. Because you cannot obtain enemy powers, the X-Buster is now incredibly over-powered against bosses. Once a stage is beaten, there is no indication that is the case and it can be repeated indefinitely. From my experience this game appears to have no end. I think it is also worth mentioning that both the X and Doppler stages lead to the intro stage, and the game doesn't immediately start with the intro stage.
There appears to be all of about three enemy types in the game. Hearts do exist, but they do not grant extra lives. This is because there are no extra lives; a single death leads to stage select. Therefore, no checkpoints exist for any stage. That's nice.
There is a password function, and it actually works. However, because game progression is either not clearly identified or doesn't occur at all, the password feature is rendered useless. Out of curiosity, I tried entering some codes from the genuine Mega Man X3 but they did not work. No big surprise.
If you ever find a way to progress through this game, you have more patience than I do. I'm not sure whether that is a compliment or not. Probably isn't.