He's certainly a good player but as many have said I think he's not United level - here's why...
Firstly, he was poor at Rangers. From what I have read, this is because his work-rate for the team was quite poor. Why might this be? Perhaps because he was a cog, part of the team. Not a big fish in a small pond. Just a fish in a pond.
Secondly, at Blackpool he DOES have the team built around him. How they play is basically using whatever he is good at. And because of this he's a big fish. I get the feeling he works hard for Blackpool not because he wants to, but because he should as said big fish. I'm not saying he's lazy, as I don't think he is, but his motivation to work may not be quite what you want.
At United, he would go back to being a cog. I don't believe (or would I ever want) United to be built around C Adam. His talents would be appreciated, but not revered (as they are at Blackpool) and as such I think he'd go back to being relatively poor. Maybe he'd be a Carling Cup Champion and when surrounded by reserve and youth players, may then show something that he has at Blackpool - but for first team, week-in, week-out; I don't think he'd do it.
Of course I'd be happy if I was absolutely 100% wrong and we bought a player for £10m who turned into an integral part of our midfield (with the midfield also being able to compete on a world level - as opposed to not right now).
I don't really understand the comparisons made from his old club, I mean he was still 20-22 and might not have been ready, certainly I've never watched him during his Rangers time...
To compare him as a big fish/small fish what ever might be logic, but still be a bit too underestimating, Blackpool certainly doesn't have that team fixed in as a team built only around Charlie Adam, they have a productive striker in DJ Campbell, his overall game might not be good but his contributing with some goals and has done well trying to hold up play and stretch the defense, they've got a good winger in Luke Varney and he'll even get into that Liverpool side with his current form.
If you've watched C.Adam, its not just about his corner kicks and his set plays and penalties, its his open play where he's long ball usually finds his team mates which give Blackpool the curring edge in attack and counter attacking...
He opens the play from him and also does a good shift defensively even though he looks a bit fat, I love watching Blackpool play with their positive attitude towards the game, they are similar to a growing United in a way where its all about teamwork and attack, their Defense is shit and its the only thing holding them back this season, they will lose 3 goals but will try to score 5 and they have a never dying attitude.
So for me, if he hasn't played for us yet, I'll reserve my judgement for now and will judge him based on what I've seen...
For what is worth, he'll definitely give our MF a run for their money