I think Sburb Done Quick is like, the perfect fanventure. Or as close to perfect as one can get. A short read, cute art, actually completed. I've reread it multiple times.

Karkat Goes to a Convention is also great. I haven't finished the last few hundred pages, but it matches the tone, humor, and even magnitude of Homestuck to a tee. (And Jack Noir's featured heavily there, and he's my favorite character, so... not unbiased.)

Both of the fanventures I recommended are really popular, so I wouldn't be surprised if you've read these already :P I'm suuuper picky with fanventures.