Eve has an unusual skill system. In a typical MMOG like World of Warcraft your character levels up skills and power as you play. Kill more monsters, get more experience, get levels. The time it takes to level in WoW is fairly predictable, but players are rewarded for being online and grinding more often.
Eve isn't like that. In Eve your skills level whether you're online or not. And you don't level faster based on what you do; it's entirely based on the clock. If I set my character to train Battleship level 3, it will take 36 hours to get there. It will take the same time whether I'm busily shooting NPCs in my Battleship or not, indeed whether I'm even logged in.
At first blush this sounds crazy; where's the reward for playing? But it works very well. I never do some boring repetitive action to level up; skills train at their own pace. I can take a break from the game for a few weeks and not feel like I've lost anything. People with way too much time to grind don't gain a big advantage over more casual players. And older characters are uniquely valuable; they've had the most time to accumulate skills.
In WoW a primary goal is levelling up; in Eve it's just something that happens. That frees the player to concentrate on more complex goals like "develop a traderoute in Megacyte that makes me rich". I'm not saying Eve's better, exactly, but it's different. And it works.