It's been a year since I've played this game. Even still, my very clear memory is that this is a very frustrating game for several hours. The platforming is awful at first. The enemies are very obtuse at first. But! If you put in the time and patience and effort, I think you will, like me, get to a game that is really really incredible. This is one of those games where I'm glad I got the first playthrough done with, because my upcoming playthrough is going to be very enjoyable, now that I know how the enemies work, how the systems work, how the platforming works. It's...frustrating reading the negative reviews of this game. It's frustrating because their irritation and frustration is very understandable. I strongly believe, though, that if you give it some time, and if you compromise with it, agree to meet it halfway, you'll find a very great, clever, and super enjoyable game. Be patient and you may, like me, find one of your very favorite games of all time.
I think people are being a bit unfair here. No, it's not the best in the series (I'd say the first one is, followed closely by the second). But I enjoyed it much more than I did the third one. I really really enjoyed the story, which I wasn't expecting at all; I was just expecting some fun acrobatics. The combat is fine. It's not incredibly difficult, and you can't really lose (at least, I didn't see a 'game over' screen when I played it). The art style is incredible and attractive. I think the cel shading works very well. Because of the lack of difficulty, it can be jarring to come into this game with the expectations of something like the first three games, but that doesn't make it a bad game. It's just a different direction. This would be a good game to introduce yourself to the series if you haven't played it before, to get yourself used to the mechanics and combat before jumping back and playing the earlier ones. Give it a (fair) shot.
I've sunk several handfuls of hours into this game over the last couple of weeks, and it's incredible. Not based too much on luck and not based too much on skill, meaning that, like Spelunky, when you finally break through and win, it's a magical run that sticks with you for a long time. Plus, there are a bunch of unlockable ships and ship layouts, so there's a pretty swell amount of replay value added to the already significant replay value that naturally comes with rogue-likes. Easily one of my favorite games of the year. Buy it.