Ultima Online, Relive the memories...
I know most of you haven't heard of Ultima Online, but it's my single favorite MMO, ever since I first got introduced to it back int 1998 or so. It was an early MMO that featured classless characters and a skill-based system where you could build up any combination of a set of skills rather than just mindlessly leveling up a character. That means what a character could do could be mixed and matched in any way (Magic Swordsman, Magic Chef, Chef Swordsman, Tamer Necromancer, Ninja Paladin...)
This also with handling weapons and equipment being based on strength means anyone can use any equipment (provided they have the skills to use them.)
Customization as well, including 'Dye Tubs' that allow you to dye clothes, Black Dye Tubs as a rare item, and special kinds of dye tubs for things like furniture and armor.
Events means rare items exist out there (I want Cold Blood, the ice blue Butcher's knife.) and high powered monsters means there's always a challenge, especially in "The Gauntlet" and dungeons.
Crafting skills are available and ranged from Tinkerers (mostly useless items), Tailors (clothing and leather armor), Blacksmiths (Metal armor, weapons, and furnitures...) and Carpenters (Wooden things, Furniture) amoung them.
One can build houses which even leads to some player towns sometimes and houses allow for storage, saftey, and allows you to set up vendors for items. The houses are just as insanely customizable, provided you can afford one.
All this and more in one massive, nearly seamless world that gives you lots of chances to explore and discover things.
I play on a free server called "Demise" here: http://www.uodemise.com/
If you wanna play, download the following:
(The Actual Game Client): http://www.uo.com/uoml/downloads.shtml
(The Client you play Demise through): http://www.runuo.com/razor/ (you load the game by loading this and pointing to the correct server. Details on the Demise Page)
(And finally, the out of date but ever useful UO Automap): http://www.uoam.net/
Read the guy's stories for some amusing tidbits about Murderous Barneys, Santa Claus, and a touching ending to his game experience.