I've been playing lineage 2 for a really long time and i've never experience hellbound properly.
What kind of server should someone join if they want to experience hellbound.
Does the population level matter?
Is there even servers where you can still experience hellbound?

Hellbound is a pivotal part in Hellbound Chronicle (duh), and during Gracia Part 1-2. I'd say Hellbound is the chonicle you should look for, since everything that has to do with endgame farming and PvP tends to happen there.

The thing is, there aren't many Hellbound servers, and the ones that you can find have a small population. It's not the most popular chronicle, and the fact that there's no such thing as Hellbound OFF files, makes it even harder.

I think a 3x (or 5x?) rates server opened last year, can't remember the name, and it had like 1.5k players, but HB servers are pretty rare.