Mega Man 5 has always been the definitive Mega Man of the 4-6 trilogy to me. It plays incredibly smoothly, the music is some of the best in the series, and the level designs are just top notch - all of this stuff is markedly better than in 4 or 6 imo. Every time I play MM5 it feels fresh all over again. I think it might be the most polished and well designed Mega Man ever - it really feels like they knew what they were doing at every step in the process after making four of these things. Just an incredibly fun and accessible game. I think it's a little too easy, especially the bosses, but that's a fairly minor complaint.