First of all, never, ever, ever refer to it as "Mount" Tremblant. It is Mont, and the locals would be offended. I would also suggest that, as an American, you display a modicum of shame on behalf of your government, regardless of whether or not you support/endorse them. This will make your experience much more easier.
Now, for the actual skiing. It is one of the largest skiable areas in North America, though not the highest elevation. It is however much better than just about anything you can find in VT, and the resort aspect of it adds immeasurable cachet. Ok, it's a little tacky (like Disneyworld / cardboard villages). And be ready to shell out the big $$, especially during christmas time. Just be aware that off-mountain accomodations will be much more reasonably priced.
Also noteworthy: it gets cold up there. No ... really: damn cold. Not USA cold, Quebec cold. Case and point: my brother is nuts, certifiable. He actually skied at get this ... -75C (including wind chill). That translates to -101 F. Only one run, but still. And this is the absolute record I've heard, and only once. And in late Jan early Feb, which is the coldest period. For Christmas, you could easily get -20C, and you should certainly not count on anything warmer than -10C. If you're going with kids, this counts.
And finally, I suggest ditching the family one evening to patronize the fine "Faucon Bleu", the local stripper joint.