LOTRO was my fist MMO. I played it almost exclusively for 2 years. I couldn't bear to play it any more, what with it having gone free to play, and having BUY STUFF WITH TURBINE POINTS! pop up every time I try to play, not to mention that leveling goes too fast now and I'm not very interested in raiding. It used to have an impressively large world, but the later additions and zones are quite underwhelming.
Then I tried Aion. It basically shrinks everything: world size, run speed, and mob aggro range. Very disappointing.
So, anyone who's played enough to have gotten around a lot: is it big? I don't even mind if questing is repetitive or if PvP is boring, as long as there's lots of room to do it.