It's fairly standard PC MMO fare, with a couple of differences. For instance, the game is VERY highly centered around competetive PVP, with an entire area set up just for it.
Characters are fairly customizable, but the real customization comes from their builds. Unlike many games, in Guild Wars you have to take two professions. One as your 'main' profession (whose basic appearance you take and have a couple of natural advantages with) and a secondary. This gives a much more ridiculous and expansive option of characters.
To give a couple of examples, you could have a Warrior / Ranger, and focus entirely on Warrior skills if you wanted. Or you could split between the two and have a character balanced in both melee and ranged combat and have a pet to fight with you to boot.
With six classes in the main game, and more added in the expansions, you ended up with some pretty insane choices there by the end of it.
(As an aside, one of my favourite builds was the cheap-but-funny Necromancer/Monk combo. Sap the enemy of strength to keep yourself alive, summon minions from the corpses, and use your monk skills to bail out your party.)
The other important part is that while a level cap of 20 seems fairly low, that's not really the case. The strength of a character is much more centered around their abilities and their gear than their level, with weapons usable based on their ability skills (which are changable in towns, so if you need to swap specialization to help a friend out, it can be really useful.)
From unconfirmed rumours, GW2 is going to keep the flexibility but have a much higher level cap, as that was one of the things that apparently turned a lot of possible 'endgame-heavy' players off.
In the first game, players were all human, but that wasn't a problem as the world was so good. There were non-human characters, though. Some of the most notable among them being the Charr, bastard children of Orcs and Chewbacca. In GW2 you'll be able to have more in the way of races.
Personally, I'd suggest at least downloading a trial version and seeing if you like it. There's still plenty of people playing, and it's a hell of a lot of fun. Plus if you like it and you get Eye of the North, you'll apparently be able to get special things from your old characters in GW2. :D