We stayed at the beginning of January in one of the 2 bedroomed apartments.
Really nice hotel - a little shabby in some parts of the room but nothing overly bad that would warrant it ruining your holiday. The apartment we stayed in was spacious and clean.
Hotel staff are very nice, breakfast is a good selection, although I wouldn't buy it if it wasn't included in the price as it is expensive.
Shuttle buses are every 30mins or so in the morning up until about 10.45am and then there isn't one until mid afternoon. From 5pm they run every hour up until about midnight. Taxi from Disney to the Adagio is 13 euro.
Less than 5min walk away is the Val d'Europe shopping centre which is HUGE and gorgeous with some lovely restaurants (cheap up to expensive) and a really large supermarket.
I do think that it is used by large groups of people - we noticed a group of US students there but they were all late teens and there was not a problem with noise where we were but I can imagine school parties etc using it so it might be best to ask. There is also no bar in the hotel.
On the whole, I would definitely stay there again.