Wow, okay. So I have to say. Wow.
I've played most of the levels, and I'm kind of stunned by the incredibly, incredibly high quality that I've seen, and the consistency of it. I have no clue who is going to win. I count... five frontrunners, maybe, and they're everything from simple platformers to story-driven series to whole games in and of themselves. Simplicity to ambition, everything is covered very well, and I do not know which will win. I will say this: do not underestimate the small levels because they can bite back and win. I could easily see a simpler level beating the series here, but no matter who wins, I have a feeling they will deserve it.
Another step forward in evolution, fellows.
If you must know the frontrunners
MP3 and Star king- even if some parts dip low, some are absolutely fabulous and showcase both people's best work. The references to past games are incorporated very well with completely original ideas.
SuperMIC- his best work by a mile- he managed to incorporate fantastic gameplay and a great story with seamless coordination. His gameplay is also seamless and thankfully bugless. He had to crunch a bit in the level using his story to cover some parts of it, but nevertheless it was a fulfilling prequel.
Nwolf- It's low key, but the appetizer of a simple, flawless recreation of the SM64 Big Boo's Haunt (and a ♥♥♥♥' piano with 118 blocks) is a perfect lead in to a fabulous Rainbow Road segment, also Nwolf's best work. It's just a fabulous atmosphere. 
Buffooner- The simple platformer that may take the day. This is literally JUST LIKE a Yoshi's Island level. Everything from the graphics to the fine aesthetics to the platforming style and every little touch you could think of, it's all there. If you've played Yoshi's Island, your heart will flutter.
Blackyoshi- With this competition he's more of a long shot, but you have to admire his two unique Yoshi's Island interpretations, with a tremendous, if not very laggy, cave.
BrawlerEX- It's a very long shot seeing as he never finished, but I kid you not, Brawler does the most original gameplay and some of the best graphics on this site. Also, no bugs! 