Well, I just beat it (100%) and, while it's definitely a lot of fun, it does have some issues. The main problems are the camera, and invisible walls (there can be a lot of them). In addition, the power ups feel like one off gimmicks for the most part. Apart from the fireflower you use the powerups in one level at the most, and sometimes even only once.
Still it's large (took me a little over 9 hours), has a lot of fun levels (although some are clearly inspired by other games), and the bosses are different every time (instead of fighting Bowser three times).
As far as Mario 64 hacks go, I'd rate this second only to Star Road, and that's mainly because that one feels more polished and is 'purer' as far as just platforming goes.