I am a weirdo and honestly believe this (or 4) is the best NES mega man game. First of all it's beautiful, they really knew exactly how to make NES games look fantastic by this point and it shows. The weapons are pretty good too, nothing too spectacular but there's some fun ones in there. The world wide travel theming is fun as well and I love how they started introducing hidden secrets in levels here.
The adaptors are fun too, this is the game I would recommend the most to new players to the series because the jet adaptor really helps ease you in to the experience. It's not the hardest game in the series or anything but I earnestly love it.

Top 3 mega man game for sure.
Weapons are fantastic (probably my favourite set in the series), level design is fantastic, music is weird since it's all electronic instrumentations but I think the arranged soundtrack is free now which is way better
The gear system is also really fun but not too overcentralising since it really feels like the game was designed to compliment them but not require them which is nice.
The only big complaints I have are that this game should have had more playable characters, the soundtrack is weird as previously stated, the wily stages are too few and too short and holy shit they are stingy with checkpoints in this one for some reason it makes Torch Man's stage a nightmare.