Pros: Huge piste area, some variety, good snow
Cons: Crowded late season, Not very pretty, No trees
Val Thorens has some of the best European piste skiing, period. Piste bashers will love the varied and interesting selection of intermediate/ advanced groomed runs. Near VT itself the skiing isn't amazing but it's well connected to the nearby areas on your 3 Valleys pass. The only real downside is the lack of tree skiing, and if the weather is bad on a mid-winter trip the exposed slopes quickly get blown clean of powder. Usually conditions are fine, but they can change rapidly, with VT getting the worst wind in the Valleys (being at the top, and most exposed).
Despite the comprehensive efforts of the local authorities, there is still plenty of unpisted terrain, some obvious (and popular) but some tucked away, and left mostly untracked. The sheer size of the available area means that despite the resort getting crowded, people are reasonably dispersed throughout the mid-day, in particular Orelle is normally quiet, and provides excellent terrain for the more advanced. Most of the crowds stay clear of Orelle because the piste map shows it to be basically empty (it isn't, the frogs lie!).