Is this a good Christmas present to gift to anyone? I would assert so. This review will be split into a few parts.

1) graphics and style
Naturally, the first thing one observes when stepping into a game is the look and feel of it. In that, torchlight provides a powerful aesthetic experience into a small package. Even though the game looks great at the highest setting, it's quality and style trickles down to lower resolutions and lower end graphics cards. There is even a netbook option for those who want to run it on the go. The spell effects are just fanciful enough to look good, but also just tastefully short of getting messy and overwhelming. Monsters aren't very special, but have sufficient variety such that you get excited in finding a giant fish, which turns your pet permanently into that form. One thing about combat in torchlight is the damage numbers that pop out over the creatures head. It gives a good kick to see a big fat critical hit pop up. On the whole, torchlight wins on graphical style.
2) gameplay polish
Everything is well designed and polished in this game. The best feature is probably something that was imported from another game, but otherwise torchlight meshes everything that is good about this genre seamlessly and smoothly into a wonderful masterpiece.
As for that imported best part, it has to be a pet that you can load up in inventory and then send it back to town to sell the goods. This has probably been one of the best inventions ever for this sort of game, and words alone cannot explain how much it remedies the usual anguish of inventory management halfway through a level.
Item design is good, with a wide variety of different equipment options as well as individual item power levels. There is even a form of item levelling in terms of continually enchanting it with more and more special attributes. It was initially too powerful but that has sincee been fixed.
Finally the bosses and level designed are tuned just finely, not too hard nor too easy, with a great heaping of variety.
3) length and replayability
The entire game is rather short, about 12 hours on hard difficulty, and if you're experienced at such isometric top down diablo clone games you would probably take 8-9 hours for the normal mode to clear through 35 floors. It is a wonderful experience for all of the twelve hours, and the pacing is just right, not too fast nor too slow.

After completing the game once, an endless dungeon is unlocked and it has infinite levels which means you could potentially play the game forever. You could also play another of the three classes and level it through the story mode, trying out new skills, abilities and strategies. All in all that would add nicely to the usual entire replayability of mindless levelling and item grinding.
4) sound
Perfectly acceptable sound reminiscient of diablo, sound effects also go well with the mood, and the ambient music sets it nicely.

5) future developments
As it is, torchlight is purported to be a 18 month precursor to the mmo ( massively muliplayer online ) it is perhaps in doubt as to whether coop functionality will be developed and patched in at a later date for download.

6) price factor
At 20 usd, it's half of any other comparable game on the market out there now. Although, this is likely due to the lack of the multiplayer portion. It is also unsure if the mod portion, torchED will leave up to it's expectations. As it stands however, the game is worth more than 20 dollars, even without all the extras.

At the end, torchlight is definitely a value for money, and will make a good and rewarding Christmas present for anyone who enjoys this genre, or are busy waiting for diablo 3 to be released.
It makes its way up there with the top 5 best christmas computer games for this year.