Some mash-ups work, others don't.
The mash-up between Angry Birds and Star Wars (which was released last Thursday) is pure genius. It is, IMHO and based on my first few days of playing it (and from the perspective of a Star Wars fan of course) more fun than the previous versions of the game.
All the fun of Anrgy Birds and all of the sights, sounds, characters, and mythology of Star Wars.
I have finished the Tatooine level and am half way through the Death Star level.
In the early levels, you get to play with Luke, and Obi Wan, and Han. Luke has his lightsabre. Obi Wan has the force. And Han has his blaster. Great fun.