One of the things I've found the most striking since returning to WoW is how extremely quiet the game feels. The server we rolled on is consistently marked as having a medium population, one that's supposedly heavily lopsided in favour of our chosen faction, but I'm just not seeing it.
And no, I'm not saying that the game is dying - save your breath. Subscriptions have dropped by several million since I last played, which most certainly had an impact on how busy the in-game world appears, but there is more to it.
The Old Republic has probably spoiled me for what I consider a high population. Ever since they consolidated everything into a handful of "mega servers", there isn't an area in game that's completely quiet, ever. Each faction's fleet (the major hub) consistently has 300+ players puttering around at any time of day. Doesn't matter which planet you go to (except Quesh maybe, since it's so small...), at least on my home server there'll always be between 100 and 200 people out and about on each.
Things aren't that much better out in the open world. Thanks to cross-realm zones, we do see other players about, but not that many. No two of them seem to share the same realm tag either, indicating that a lot of different servers have to be squished together this way to create the impression of any kind of activity. It also feels like the number of player characters that we run into (regardless of server) keeps dropping the further we advance in levels, CRZ or no CRZ.
I reckon that the active players that are out there are all hidden well out of sight of our lowbie characters, presumably chilling around some new portal hub in Pandaland (feel free to enlighten me). Flying mounts are also good at making people invisible to those who are ground-bound, and it's only every now and then when someone suddenly swoops out of the sky in front of you to "ninja" a gathering node you were making your way towards that you realise that there's potential for a whole additional layer of players traversing the skies above you and never interacting with you in any way.
It's certainly a far cry from the bustling MMO world that welcomed me with people all around me seven years ago (and back then the game actually had fewer subs than it does now).