This is going to be a very long post, but I'll give my opinion it.
I guess I'll start off with its history. Mega Man games haven't been made at Capcom, and this was the game by Inafune (former Capcom employee) to stick it to Capcom. They began a Kickstarter to help bring back that classic goodness that fans wanted. The video channeled a lot of that energy and even did a good job on making people fond of the series fund this kickstarter (me being one of them). While being very successful, things took a snag, problems happened. Stretch goals were created but people wondered if this was all feasible. Being ported to so many consoles, people wondered was this really wise? Also people weren't happy with the game's art direction not looking like one of the proposed concept art for the game. They didn't promise that it'd look like that, but the actual game did not look pretty.
The game got funded and even reached over a million dollars from what I remember. We were waiting for it and more bad things happened for the team and how it was perceived. Game got delayed, Inafune announced another Kickstarter (Red Ash) before MN9 was completed, Inafune discussed talks of a sequel and other media, it was poorly handled. When the game was finally set to release, it received another delay. Network problems made them delay it, a stretch goal most didn't care for. Everything else was completed, but it couldn't be shipped. The game finally released and I guess I'll give my impressions.
First off, the game is not awful. But it's not the game that it lived up to be. After 3 years and over a million dollars, it doesn't live up to people's expectations. Visually, game is still ugly. I can get past it, but it is what it is. The problem is it didn't need to look visually amazing, it felt like they were just being sloppy with it and didn't care. The gameplay? It's alright at best. Dash mechanics by killing enemies with it doesn't interest me. Infinite air dashing ruins some platforming. Level designs lack a lot of polish. Enemies aren't too interesting and the diversity isn't quite there. The game mostly relies on cheap deaths rather than something more solid or fun.
The stages aren't too fun to replay. The stage design just feels mediocre while being littered with a lot of ideas that harm it overall. I'm actually pretty good at Mega Man games, so I had no issues completing the stages, personally. The stages just feel more like a chore if anything else though.
Overall the game isn't awful. Even ignoring the history that plagues this game, I don't think it's anything exciting. If I had to sum it up in one word, it'd be forgettable.
Mighty No. 9 lacks the charm of a Mega Man game. The game is already a knockoff of the Mega Man series, but it's unfortunate that the gameplay had to feel like an inferior version of it too.