The premise is that aliens give humans a test to see whether they're worthy of joining them as galactic superior beings or if Earth will be destroyed. They gave one random human (Simon Pegg) the ability to do absolutely anything by simply saying it and then waving his hand. That sounds like possibly a fantastic premise for a great movie -- the problem was the execution.
Simon Pegg is given the power to do "absolutely anything" but does basically nothing with the power. He uses it for a few comedic skits, to help his daily life, to chase after a girl, and to fix problems that arise. That's pretty much it. He hates his job, so he just makes people be nicer and listen to him more. How about you get your dream job or just become independently wealthy, but for some reason he never thinks about that. He's a writer, but it mentions multiple times that he has problem of thinking of a wish. Even though he previously found a solution to that problem, he never uses it again. The character's intelligence and decision making are what mainly ruin this movie. He's given basically infinite power, but it's basically just a "get the girl" movie.
He can become a superior being himself, augmenting his anatomy/mind. Nope. He could restructure the world to become a better place. Nope. Hell, he could be selfish and make his life the best possible. Nope. Let's just do some random ass wishes and desperately go after a girl who you've barely ever talked to.
The wishes sucked, the romance sucked, and the ending sucked. It's basically only enjoyable if you're using it as background noise or can go mindless for an hour or so.