I played a couple of hours of it yesterday. Graphics wise I love the animations and how organic everything is. A lot of effort was put into making it feel alien and it shows, it is absolutely fantastic. As for the gameplay/level design it was very good and very metroid like. I wouldn't say this is an entry level title on the series (and it shouldn't be) but I have made progress without much trouble and it was a lot of fun.
There is one thing that bugged me right at the start. There are foreground ladders that are only cosmetic. I would change those graphics so they don't look like ladders...
Also, a complaint of personal taste that is a minor spoiler:
All in all, this raises the bar in rom hacking quality. I'll reserve some time to play it to the end.