AO ( basic, no expansions ) is currently free for a year, if you sign up before Jan 15th. The sci-fi setting was what got me interested, not having tried a mmorpg before, although it's not particularily sci-fi other than the labels.
http://www.anarchy-online.com/free/ad_campaigns/freecampaign/
Is it any good, though?
Uh, I have absolutely no reference points. It's a bit dull if there's only 2-3 of you together, I'd expect it'd come more alive if you joined a guild. Ppl seem to think it's better than SW Galaxies, which is the only other Scifi-themed morpg I can think of. The Shadowlands extension pack got very good reviews, but that isn't free & the trial is something daft like 7 days.
Anyway, it's free, try it yourself ;)
Been playing it on and off for a while... got to say it's *big*, almost overwhelmingly complicated as you try and take the system in and the sheer amount of stuff. Actual things to *do* can get a bit repetitive, but I guess that's the same in any of these games.
The free trial is open until next year now, so there's no problem trying it out for a while.