>>1001232
Honestly I've never felt the need to mod Mega Man games. They're good games that don't usually get butchered in translation. I prefer the Japanese names of characters, but nobody seems to care enough to mod the games to give them new translations just for that.
That said, if translations count, like Rockman & Forte on SFC, then check out Rockman & Forte: Challenger from the Future on WonderSwan. It's the next classic series game after Rockman & Forte, and the last one to come out before the long gap and the retro revival that led to Mega Man 9. It's a pretty cool game. A bit easy for my taste, but it's a few more classic Mega Man levels, and I like that.
As mentioned by the post before mine, check out the Rockman World DX romhacks. They take the Mega Man games for Game Boy and give them Color. Especially if you overlooked the Game Boy games in the first place, you should definitely play these. The Game Boy games are good. I - IV reuse bosses from the NES games, but do have new levels. V has new levels and new bosses. Challenger From the Future sort of feels like the sequel to these games, being essentially one last Game Boy game, since the WonderSwan was essentially a successor to the Game Boy, made by the same guy and all.
The guy above me also just seemed to be recommending regular games and not modified games. In that case, just play all the Mega Man games in release order, regardless of series. They're all good throughout the '80s and '90s. Even the more obscure ones, like Mega Man Xtreme and Xtreme 2 are good.