The original Super Mario Bros. Crossover took the internet by storm a few years back when the creator, Jay Pavlina, posted a Let's Play of him playing the game. His humor got people watching the video, which made people want to play the game. You can see that here if you haven't. And if you haven't, you're missing out. Be warned, the language is vulgar: https://www.youtube.com/watch?feature=player_embedded&v=ZGIIkDkJP3U
The game is now in version 2.0, which has more settings and characters, but 3.0 seems to take it to the next level. Pun intended.
Jay Pavlina and the crew at Exploding Rabbit are also making an "original" game called Super Retro Squad. It was successfully funded on Kickstarter last year. I say "original" because it's based on SMBC, with characters like Manni and Lanzo, two German Miners who find themselves in the Asparagus Kingdom and have to save Princess Apricot. It's obviously staying true to the roots of the characters in SMBC, but this gives them the ability to actually make some money off of their work. From what I've read, development is going to kick into gear after SMBC 3.0 launches.
http://www.kickstarter.com/projects/explodingrabbit/super-retro-squad
Check out all things Exploding Rabbit at their site:
http://www.explodingrabbit.com/
These games are great. Really illustrative of how your verb set in a game is just as important as level design.
Added to my backlog.