Megaman/Rockman 7 really isn't bad, it's just different while still sticking to the familiar system without odd or too-drastic changes. As we've shown, a lot of people here seem to like it and probably liked it back when it came out too. Not my favorite game, but it's better than others in the series for me.
This is just theory from seeing some of the more vocal hate years ago in other places, but perhaps the reason why some people give it so much crap, aside from the bigger and sometimes awkward-looking characters, is that at the time, it wasn't Megaman X. Even for what 7 brought to the table in terms of new features (which the X series would semi-replicate on their own accord, like the Shop system finally being implemented as of X8 and even sooner if you count the Xtreme titles), X was the leaner, meaner, faster and more 'badass' thing at the time. Who gave a whatzawhosit about Rock's sliding and Rush Coil when X could just scale the wall and then dashjump a gap with precise ease? Super Adapter? What's that, I can't hear you over the armor ability of charging every single Maverick weapon!
Of course, in retrospect and hindsight, people are more willing to separate the two now and see them for what they are, which is why 7 is seen a bit more positively nowadays. Most of the hate's shuffled onto 8 in recent years for its more questionable design choices, or Capcom's second cash-in of the retro craze via 10 (or Capcom in general, but that's beside the point).