One thing I can say is that the load times are pretty long. And you can't switch weapons within a level so it ca be frustrating to wait through a couple load screens just to change weapons.
Also, I would have really liked more run n gun levels, they're a lot of fun. But for $20 I think the game has plenty content especially if you're gonna try to get S ranks on the levels. Theres potential to put lots into this game to make some epic runs through the levels. I look forward to seeing speed/perfect runs after people have been able to master the game.