Mix one part World of Warcraft, one part Diablo, one part Guild Wars, and stir.
The game blatantly rips off Diablo and the other above mentioned games, and it has fun with it. The NPC's all talk humorously, using awkward old school English, and some of them have Sean Connery or Arnold Schwarzenegger accents. The item names are comical as well, such as Tainted Baby Seal Skin Greaves of the Platypus.
The gameplay is very diablo-esque, and quests are given out World of Warcraft style, right down to the yellow question marks and exclamation points over the heads of npc's who have quests to give or rewards to give out for quests completed. It's like Guild Wars because the towns are where you meet other people to form parties, and all other areas of the world are instanced just for you and those who may be in your party.
After a few hours with it, I gave in and paid the 5 bucks a month membership fee so I could store items in the bank and equip the best items. I figure if I get tired of it, I'll just cancel...and for 5 bucks a month it's worth it for the fun I've had already. Many people level up to high levels without becoming a paid member with no problem, so it is not required ot ever pay for it...it just makes things a bit nice for you.
There are some things missing, like a way to trade without just dropping stuff on the ground and hoping the other person is honest. But all in all, it's fun and addicting for what it is.
If you like these types of games, download it and give it a try. What could it hurt...it's free!