I've been playing Eve Online for about two years now and I recommend it if you are into sandbox type gaming. You really have to set your own goals there as noone else will do it for you. You also have to look after yourself for the same reason. Anything goes if it is done by ingame means and is not exploiting/hacking. Meaning that if you get scammed by someone or killed then noone, aside from your ingame friends, is going to help you. A game for an enterprising individual who knows what he wants and has a plan.
As a bonus the subscription numbers rise slowly but steadily, the game takes place in a single game world, no separate servers, and all the expansions are free of charge.
On the negative side, the learning curve is best illustrated by
this picture . Also when 2-300 players (per side!!) face off eachother in large scale fleet combat in 0.0 space the local starsystems can get rather laggy.
I've also been playing WW2OL for the past few months and it's excellent as well. As realistic as it can be without scaring off 99% of even the most hardcore fps/ww2 enthusiasts and fun as well. Learning curve is steep though and it can be really frustrating as often you die without even knowing what killed you.
Both games are team oriented, both games are best when you end up in a good group, both games have trial periods.
edit: Oh and both games have an above the average average player age, which doesn't mean that there aren't any smacktards and 13 year old idiots, but there are a lot less of them than in wow.