Klaus: Yes, many brilliant players have gone to clubs where they for one reason or another didn't become a success despite their talent. Henry and Vieira are other examples of that. But there are at least as many examples of players having a purple patch which they're never able to reproduce and I think Kagawa falls into the latter category.
Clrnc: Regardless of his position you're in denial if you don't think Kagawa has been hugely underwhelming in his time with Utd. Bar one hattrick against a poor Norwich side he's done absolutely nothing in England so far which makes him a flop for 18m. At least Arshavin who Boss compares him to racked up assists and goals in his time with us.