Online pick:
Return to Castle Wolfenstein: Enemy Territory
I've played it on and off (mostly off in recent years) for maybe 20 years now? Still a pretty active online community with lots of servers alive and well. Still fun.
Offline picks:
Dragon's Dogma II
Pretty much the most ideal open world RPG for me so far. Maybe only a few hundred hours of gameplay here, but to me that's basically forever.
(Well, maybe forever if Capcom released some actual DLC :') )
Shadow of the Colossus
I love just going back and visiting this world. The feel of the gameplay and aesthetic is still unlike any other for me. Possibly influenced why I like Dragon's Dogma as well (running around beautiful places and grabbing onto huge monsters to slay them before meeting a tragic fate myself).
FFIX
The Place I'll (always) Return to Someday. One of the only story heavy RPGs I could really play over and over, just to experience the world and characters again. The ability learning is like actual crack to me, too...
FFX
Really, the same reason as FFIX, it just has a different place in my heart. Spira is definitely my favorite world. I've played FFX several times and always revisit it every year.
Valkyrie Profile 1&2
For different reasons. Both have worlds that I also fell in love with, with very deep gameplay. I play VP1 once a year or so.
Vagrant Story
What can I say, I'm a masochist of some sort lol. Also it's a Yasumo Matsuno and Alexander O Smith production....in other words it's an ideal game to me. I can watch the cutscenes over and over.
Guilty pleasure pick:
Tokimeki Memorial Girl's Side (PS2 or DS)
Hahaha really. It's fun to play every few years. I've done every route and seen probably every event possible but still like to see how many bombs I can get to go off by dating the teacher and pissing off every boy (Himuro-sensei my beloved)