You'll find some very helpful information in the sticky post at the top of this forum.
Each server varies, some are RP, some are PvP, some are Station Exchange (buy gear for real money). I can tell you that Najena is a strong server with a bustling population.
The EQ2 crowd is pretty mature and helpful. You won't find any OMFGLOLOLorZorZXZ!!11ONE! in chat. If you do, it's squashed pretty fast and that unfortunate individual will have a hard time finding any adventure buddies.
The next expansion is due in NOV06 and there will be no increase of level cap. That has made some of the old players with maxed out characters start new toons. There is also a steady flow of new players, so there will always be folks in almost every zone.
On an average night, you can find anywhere between 20-40 players just in the newbie zone.