We found the Mercure a good choice - it really is ski in, ski out (from immediately outside the reception front door), the rooms are large with plenty of storage space by French Alps standards, the food is of good quality, and the dinner bed and breakfast works out to be good value.
The restaurant gets quite busy both for dinner and breakfast - we never had to wait for a table but can be quite crowded (and short waits at the self-service buffet). The tables on the upper floor get quite warm, and you have to take the stairs each time to go down to the buffet. An alternative for a quiter dinner if you like that is to go earlier before it gets busy. The food is good and the service friendly.
The hotel has free internet access (although we found occasionally not working for short periods at busy times).
Vehicle access is very good (once you work it out - the hotel road entrance is inside the car park - which seems to always show as full at the entrance although it's not). If coming by car, you can stop to unload right at the door to reception, and if you are lucky, or reserve a space with the hotel upfront, can park a few metres away.
The hotel is a good choice if you do not want to stay for a full week Saturday to Saturday - they seem to just book by the night so you can choose when and for how long to come.
Belle Plagne as a resort is not the liveliest (which is probably a cause of the high proportion of families with young kids at the hotel). Other than the hotel bar, which is nice but quiet, we found only one real bar in Belle Plagne (plus three restaurants which double as a bar in the late afternoon). The gondola to Bellecote runs 'til late (1 am I think), but we found only one more bar down there.
La Plagne is reasonable skiing for intermediates, not so much for beginners. Some very nice red runs in Vallendry (to which La Plagne is linked).