For me, (though I love the talent of Hazard), I'd be disappointed if we didn't sign Kagawa. He can make the simple pass or the 'killer' pass. The latter is something that I think we've been sorely missing over the last couple of seasons, Giggs aside. From what I've seen of him, he is a tireless worker as well. I think that he would add versatility to the squad in addition to an infusion of youth and talent. Obviously in the Dortmund system he has played a roaming role as an attacking mid / deep lying forward, but personally I think he could slot in several roles depending on our formation / tactics. I think he could play the 'Giggs' role in midfield of a midfield 3 (quite seamlessly IMO). He could be used as an attacking midfielder at the top of a midfield three, play behind the striker and do a job on either wing.
In any of these roles, he has goals in him, whether it be the killer pass or a goal himself. Technically I see him as a very astute dribbler as well. Most importantly (for me) he seems extremely two footed which, at certain positions on the pitch we seem to lack. I like him, a lot. I'd be disappointed to see him go to Arsenal whom I think he'd be great for when I think that he'd be able to play in several roles with United and give us some of the creativity that we have all been clamoring for, in abundance. I'd add that Hazard or no Hazard, I don't think they would be in direct competition for a spot regardless.