Guild Wars 2

Many thanks to all of you and your quick, detailed replies! By the looks of it, I will, at least, be trying to level up a new character since going back to my Nord Necromancer is a tad too overwhelming atm. If all goes well, Heart of Thorns will be on my purchase list.

Greetings. I bought Guild Wars 2 on release and had a blast playing it for a few months. Got my character about 3 quarters through the leveling process, played quests, unlocked vistas, did some PVP. Just enough to get a gist of the game. I had to stop shortly after and followed events only from a distance. Now, I have the chance to jump back in and, with the base game being free to play, potentially convince a friend to join me.

I’d like to know the following:
-are there enough people leveling up as to have a fun leveling experience? (doing area events and all that jazz)
-the living world events that I have missed (meaning, all of them), is there any way of playing through them or is that content which isn’t available anymore?
-how is solo and duo play?
-in general, would you consider it worthwhile for someone like me to return to the game after all this time?

In case some questions are cloudy, I’d be glad to clear them up. My english is a bit rusty at the moment. Also, I’d like to thank in advance anyone that takes some time to answer my question. All the best.