Descent is one of the best buys I have made in a long time. I'm an old-school dungeon crawler, with my roots in games like Hero Quest, which whiled away many hours of my youth. This game is what happens if you take a game like HQ and ramp it up about 10 levels of awesome.
The game is expensive, yes, but the components are of extremely high quality. I've probably put over 100 hours of play into this game in the past few months and the pieces are still holding up remarkably well. The plastic figurines are durable and look really cool, especially when painted. There is an excellent variety in both heroes and monsters which keeps things fresh. The customer service from FFG is also very good; I discovered a missing figurine from one of the expansions and a replacement one was mailed to me within a week from FFG
There are about a billion pieces to this game (by far more than to any other I've ever played), and you definitely need some kind of sturdy storage box with a good filing system to keep it all organized (I use plastic baggies). The game is also very long; I'd say an average of about 4 hours for a single quest from set-up to take down (although depending on the quest I've had some go for as few as 2.5 hours and others for as long as 6!). It can get a bit tedious at times, especially in the longer quests, but if you have a strong Overlord player, the pace of the game can be managed well depending on the skill level of your heroes.
The biggest downside to this game is that it is horribly, hideously unbalanced in favor of the Overlord. If you have an Overlord who has a good grasp on strategy and play using the default rules, there is no way the Overlord will lose. It's a bit ridiculous, really. The good news is that it's easy to fix that; I've instituted some house rules that balance things out nicely. It took a fair amount of time and effort to get to the point where the game is balanced, though, and that was a bit annoying to say the least.
Overall this is an excellent game, although not really one for a casual gamer with the steep price tag and very long play time. If you get into longer games, though, Descent is an excellent bang for your buck and will keep you entertained for a very long time.