One of the most distinguishing features of Eve that sets it apart from many other MMO games is that there are no classes. Much like real life, you have characters and careers that they can pursue but change at any time.
Over on Andrew's World of Warcrat blog Of Teeth and Claws he gets into a debate with Tobold over whether or not the "hybrid" classes of Druid and Paladin are too powerful (or rather too flexible compared to other classes) because they can do any part of the "holy trinity" (i.e. Tank, DPS, Heal) effectively depending on the specification they have chosen. This allows them to access more raids I gather from the posts.
This got me thinking how in Eve players are not restricted to roles except by their own choosing. Depending on the ship you pick and the modules fitted on it, you can fill any roll in Eve's combat (Tank/Tackle, DPS, "Heal") as long as you have the appropriate skills.
Of course, that's the catch: your skills train at a rate that cannot be increased by time invested in game. So a WoW player could grind levels for a short week and have a decently equipped level-capped character while an Eve player skill can't fly a basic Cruiser decently in the same amount of time. The WoW player could conceivably grind multiple characters in different classes up to cap and the Eve player is still considered a horribly inexperienced newb.
Speaking of level cap, the optimal training plan and character attribute distribution means that someone could train all Eve skills in about 4 years. Just thought I'd throw that out there.