In short: the game is pretty much the same way as you left it. The only updates that occur are for automation purposes.
-The last skill update was before you left.
-There are certainly still people playing, though they're focused around certain activities/areas, i.e, you won't tend to find people in random out of the way outposts or be able to just casually group up for missions. I don't think the situation is any different to how it was in late 2012 though. Joining a guild is recommended.
-In terms of speedclears, teleportation skills act the same as shadow stepping in that they won't allow you to jump to inaccessible locations. Again, I don't think that's a recent change.
-The market is certainly still functional, though it may take a little while to get used to current prices and such. Other people could probably elaborate.