City of heroes/villains is a casual game. You can leave it and pick it up a few months later without being left behind. And it's a pretty basic (easy) mmo. It's a great starter.
Vanguard is the polar opposite. It's a hardcore mmo. Harsher death penalties, longer time to gain levels, quests are not basic. The only time you could potentially drop it for a break is when you reach the level cap. If you sit out of an expansion (like many of SoE's games) you should pretty much call it quits for that game.
Lineage 2, for me, was very boring. There wasn't much to do between levels. I only played it for a month before I moved on. So I can't really give a fair rating of it.
If you're looking for something more complex than CoH (WoW) but not as intense as Vanguard, I'd say go with Conan, EQ2 or FFXI.
