Have been to St Anton about 6 times in last 4 years, twice staying in Oberlech, and love the place. Whilst you could argue that some of the mega French resorts have better on piste skiing, they in no way have anywhere near the fun factor. The skiing is awesome and the off piste looks amazing (never tried it as I'm not quite good enough).
There are a couple of negatives about the skiing - 1) some undergraded blue runs, which can get pretty steep and very busy mid afternoon (the main run back to village via happy valley). These are only minor negatives but timid skiers should beware and maybe stick to the Rendl section or to Lech/Zurs. 2) lack of tree skiing, which in poor visability means that you have a lot of flat light.
Despite the numbers the queues are pretty minimal, especially since the installation of the new Galzig gondola.
The skiing is only half the fun though. The apres ski is without doubt the best. I tend to favour the Mooserwirt over the Krazy Kanguruh, but that's only because I have come to love the cheesy German apres pop that gets blasted out (sad, I know, but you'll appreciate that once you've been). Even took my 3 kids there for an afternoon this year and even they loved it too. The Griabli accross from the Mooserwirt used to be our favourite haunt as they had a great rock/soul/blues band called The CCJ's but they split up a couple of years ago and they haven't been replaced, although bumpped into one of them in March and he said that they were getting back - fingers crossed then. After several beers, ski down in the dark (not to be missed!) to Post Kellar (Hotel Post in main st) for Gunnar - brilliant German singer/musician. The place is jumping till around 8.
The mountain restaurants are all good too, although there could be more of them. Oberlech is a lovely spot to lunch if skiing in Lech. I have stayed at Hotel Montana in Oberlech a couple of times ond the food there is the best I have ever tasted.
Innsbruck is best airport to reach St Anton and is now only about an hour away thanks to a new tunnel.