I'd say it is a bargain.
Age: 24
Versatility: his solid defensive-MF performances, coupled with his very convincing attacking forays.
Comparisons: when it comes to the English Central MF pecking order, he's only got Lamps. and Stevie G ahead of him. Not bad by any means. He is similar to the role Scholes used to occupy at various times where he pulled the strings from the centre of the park.
Suitability: For starters, he's English. He's been around the EPL set-up and won't have major problems settling in, which gives him the distinct edge over Diarra/Gattuso/Mascherano. Plus, I'm guessing McClaren would be clever enough to draft him into the national team on a more regular basis. If Gerrard is given a more attacking role from here on in, or if they make do with the idea of having both Lampard and Gerrard in Central MF, Carrick could become a mainstay in the defensive MF positon.
There's more, but I'm being distracted by the Swannies at the moment. In essence, 14m quids, and a 4-5 year contract = a lot of future benefits for MUtd.