Sorry, but I don't buy that. Mega Man games are still well made. Sonic games are poorly produced.
Mega Man games in the Zero/ZX series are still solid productions with great gameplay, graphics, and music. IntiCreates did an amazing job with that series and moved 2D Mega Man games in the right direction: open, Metroidvania style worlds with exploration and the ability to finally play as bosses. Couple that with some great art direction and a fairly cohesive plot, and you're definitely in business.
Hell, even the Battle Network/Star Force series is good. Is it traditional side-scrolling Mega Man? Of course not; it never attempted to be, but people hate on it for that reason anyway. It's a series that combines real-time battles with the customization aspects of popular collection RPGs. People seem to get their panties in a bunch whenever Capcom makes another BN/SF game, but c'mon, this is Capcom we're talking about. Slowly evolving a series through sequels is their M.O.
It's been a long time since Mega Man games sucked. I think the last one in the series that we could actually say sucked was X7. That was years ago.