Getting a little tired
I'm a big fan of the shift games. They're an example of a great flash franchise. They're simple in their execution and graphic - but the concept and the humour really carries them.
I do feel that the series is starting to get a little tired. There is only so much you can do with the idea. To be fair in each version you've added something new to the concept, but I'm not sure if they always add to the game. I felt like I was playing two different games - shift and a multiple person puzzle game. I don't think they gelled seamsly.
It also seemed to be lacking some of the humour we're used to, which is a shame. I liked the opening cut scene, although I'm not sure if it was necessary for this kind of game. The puzzles were clever... the music was good.
I just feel, having played the other games, that the game is starting to get a little old, and the concept a little worn, but there's no denying that this is a strong follow up game.