I personally played Lineage 2 a lot on retail, and private servers, (currently playing WoW) but if you were to go retail id say its past its prime, and the community is at low populations compared to WoW.
L2 will definitely take up a lot of time (leveling is much longer than WoW, and essentially no one does quests) if thats what you are looking for, from the class change quests, to sub class quests and 3rd class change quests (
) and then leveling it all over again for the sub class.
Best things about L2 though is the open pvp, kill anyone you don't like looking at you, massive pvps, clan wars, castle sieges (really fun imo). Also manipulating the world to affect others - Bored? Go ruin someones day! Buff mobs that people are attacking, train people with mobs etc (chance for them to drop their gear for your benefit). There is a chance you will lose gear or inventory items if you die by a monster, and you also lose experience (~4-5%), you will not drop any gear if a player kills you, unless you are "red" aka chaotic because you just killed someone for no reason and havnt "worked off the karma" yet by killing mobs.
At this point would be pretty hard for you to catch up with all the players who already are in top gear, ebaying might be an option...
But anyways I recommend L2, definitely a lot of fun and very social/political with all the things you can do to people
Bad thing with private servers is most of them have the game so skewed, some have edited classes, skills dont work like they should, some have easy donations (to keep server alive) and hence kids got weapons and armor that will rape you unless you donate. Although the most fun ive had is on private servers, but those were C3-C4 servers a while back. Id try to find a server that is near like retail and not too crazy on the donation side with a good population to test it out!