EVE is an amazing MMO. It's the only one I keep returning to, every time I miss its incredible depth.
And then I slowly get bored. But hey, it still keeps me entranced longer than most of the annoying MMOs on the market.
And I second the coolness of the economy. My last stab at the game, I rolled a manufacturer - I'd never considered producing items before, and I decided, "Why not?". After getting a few of my skills up, I started loving it. The biggest problem (benefit?) is that it's very non-interactive. You place an order, see that it'll take 24 hours to produce, and that's that, you can log off/go mining/shoot some rats. Once your production run finishes, you dump your product on the market, undercut your competition, and maybe check every few hours to see if someone else undercut you in return. If you're planning to do nothing but economic manipulation, you're going to get bored. But it takes surprisingly little time to get the basic skills (I think it took a month or so to get most of the essential skills up to either 4 or 5), and once you've got the basics down, it's a great way to make money
and keep yourself supplied at the same time.