I didnt' see an introduction page, so I'll do it here :).
I go by Bloodmorphed. And I have never played a Lineage game, ever. I am curious as if I should start? I hear good things, but I hear even worse things. I doubt the people saying stupid stuff have any idea of what they are talking about, though.
Secondly, If I do start, I would need a mentor plus a clan (or guild?)
I can only play on weekends, and the chances of me playing every weekend is pretty slim. So I'm super casual, but will play a lot when I can.
Lineage 2 is a game you hate or love. It depends on what kind of player you are. Fast walk trough:
Clan: You can get into an academy of a clan for the academy tiara that boosts your experience abit when its equipped. You are free do join any clan anytime, but in the mid levels, you may have to accept clan war situations that slows you ability to level in the open.
Level 1-76 (no-grade to S-grade)
You simply follow the quest series called Path of Awakening. You spend a few hours every day doing the quests and grinding some monsters.
For each new Grade level (20, 40, 50, 61, 76) you get a 30-days weapon and armor of choice plus some consumables.
Those can be claimed by logging in to the Path of Awakening part of the website. It will take you about two weeks playing somehow actively every day to reach 76.
Buffs: You get one hour buffs from the Newbie Guide NPC in towns.
Mentoring: Its not super important but grants you some extra experience bonus.
Level 76-85 (S to R grade)
Keep following the Path of Awakening, it gets a bit slower now. You will start to understand the meaning of grind and patients. Keep exploring the Path of awakening map on the website. Do daily quests and try to build up a social network.
Level 85 - 95 (R/R-95 grade)
At level 85 you do your last class/job change. You get a set of armor and a weapon from the NPC. Now you can start doing some of the new 85 daily quests that kicks you up a few levels more, after that you will start to change your path of playing since it gets much harder, and nothing is given to you for free anymore. Here is where most new players loose interest if they didn't find themselves a social part inside the game.
I would suggest you test it out. Its free to play and the only this you loose is time ;)