I'm trying to think of amazing stuff Manchester has that nowhere else does, but there's not much really. The arndale centre is just another shopping centre. Pretty large thesedays containing all the shops you'd expect, as well as a europe's largest Next tagged on the side, but still just a shopping centre.
Two million pubs, bars, etc. some better than others, and so forth. Britain's protection is the place to go for whisky, and Temple bar is fun because it used to be a public toilet and is microscopic in size.
If I gave a toss about culture I might think of some cultural stuff to point you at, but I'm not, so I won't. There are lots of coffee shops. Lots. I like cafe nero.
The most notable non-standard thing I can think of recently is the giant real-snow ski slope they just finished building next to the trafford centre. I've been, its good, massive, and freezing cold.