My current location in northeast America only overhypes an artist if they release a shitty pop anthem with a by-the-numbers dance beat behind it. The fact that bands like alt-J get nationwide recognition in England is the reason why I'm studying in York next year. Indeed, the album isn't perfect and is nowhere near cohesive as a whole, but it's definitely something wonderfully different from a lot of sounds out there now.
You'll love York! It's such a lovely place, plus Leeds isn't too far either if you're after some city action and nightlife.
I'm not saying the album is bad by any means, but it's still incredible underwhelming when so many better and more interesting acts could have won or been nominated - particularly with such a vibrant (underground) music scene happening in the UK currently. The situation is comparable to the ridiculous success of Mumford and Sons, as the band could be considered incredibly mediocre and commercialised in comparison to their peers of the genre. On the other hand, an optimistic perspective of this is that at least it's shifting the attention away from generic chart fodder and towards styles of music that are usually less recognised ... which is essentiallly your point!
Phew. Slightly off topic, but if you haven't, check out the winners of the Welsh Music Prize this year - Future of the Left. It's a shame their album won't get as much attention as the Mercury Prize winners, because it is outstanding. (Although completely different and probably not suited for the Mercury Prize...)