I had actually came back once before, right after the Luminous class came out. It was still pretty grindy, but since the RED patches it seems Nexon has made it much easier to level characters. They've changed pretty much everything since the last time you played (especially if they only had the original 4 explorers). I played right after it came out until 2007/08 when Lunia came out
I don't know if it's just me, but it kind of feels like a solo game until later levels when you do expeditions unless you play with friends.
"Light" here on the forums is very helpful to returning players, so I would definitely ask him if you come back.