This hack has a lot going for it. In most cases it feels rather vanilla, but it has some fun ideas and looks fantastic most of the time. There are several courses where the music pick is absolutely perfect, C9 and B3 being my personal favorites. C3 is a common highlight, and for good reason as it's a fun concept in a decently large level that manages to avoid being labyrinthine and poses a fair challenge for the progression point it's in. C5 is also a soft spot of mine, taking a stage exclusive to SM64DS and expanding it into a full level, and while the music is a bit loud I'd say the level does the job it sets out to do. C9's a fairly standard stage (funny, given how the hack's original C9 was an absolute nightmare) but I highly appreciate the SPM reference. I love B3's concept - I'm very much a sucker for when the final level is a medley level - and for the most part it's actually a rather fun stage to run through aided by its amazing music choice... save for its representation of C9.
Omega Mario 64 has some high highs, but its lows are dreadfully low.
In fact, I'd wager B1, C11-S3, C13-S6 and B3 alone are enough to make the target audience want to throw their controller and give up on playing this. To say nothing of C14, but at least that's optional. These levels are such horrid difficulty spikes that come out of nowhere, requiring very precise platforming where a single misstep means death (and in C11-S3, you have to do it in the dark), when the game is a fairly casual experience for a vast majority of the game - it's especially strange for the middle two as C12 is a stage where you'd almost have to be trying in order to die (which in of itself is strange seeing as how it's placed in the third overworld section).
C2 is inoffensive by itself, but it's very bizarrely hidden; there's no indication of where it's located and the warp is somewhat precise, which resulted in me trying and failing to enter it for about 7 minutes.
C9 is a fine stage overall, but there are a couple spots where you can get stuck in the ice crystals and need to reset the level.
This is very minor, but C13 tries to add lore that the final boss's dialogue, C15 and the 100% ending try to expand on, but the connections are very vague and feels rather disjointed, making the latter a rather anticlimatic payoff.
Not only is B3 visually disorienting, being black and white with strange textures, but it also has a very brutal platforming section - where again, a single misstep spells death - near the end of the level, which serves as a rough chokepoint.
C14 is a recreation of one of the hardest levels from a much harder overall hack, which is certainly a choice to make seeing as how it'd chase away the casual audience, while the audience searching for a more intense challenge have to wait until the very end of the game to reach this point. Having played the original level this was based on however, I'd much rather play C14 than its origin, as it compacts two levels into one and makes some tweaks so they're not nearly as obnoxious.
This may be more in-depth than it needs to be and comes off as very cynical, but I played this hack with my friends and by the third overworld section they grew extremely frustrated with this game, hated it and wanted to quit, which I find disheartening as I could see the promise this hack has and how close it was to being absolutely great, but a mere 4 stars were enough to sink their entire mood and outlook on this hack, and that was BEFORE we found out that the hack's original C9 and C15 were much more brutal than the version this port is based on. I suppose this review can come off more as a warning, but I truly did find enjoyment out of 90% of this hack, so I hope the other 10% isn't enough to scare most people off. I at least 100%'d this hack - that's a lot more than I can say for several others I've played.
If you still didn't understand, fell free to send me an PM and I will try to explain in an different way