Spent a couple of hours with HLL last night, almost all of the time dying in seemingly random ways. In a weird way I quite like that in a FPS: the confusion and lack of situational awareness seem to me to be quite realistic. I do find that usually that begins to clear up as one learns the maps, what the enemy looks like and the game mechanisms. I logged many hours in DH and RO2 and thus got relatively proficient as a grunt in those games - whether or not I have the stamina to get there in HLL (or PS, or Squad - I've got them all) remains to be seen.
To answer Grim's question, I'd say you could play these games without comms, but it would be tricky. People do tag onto a squad without uttering a word (there is text chat), but a half-decent squad leader will talk to you and may expect a response. The"over-serious player" question is difficult because you won't know until you join the squad. There may be some clues in the server description, but I guess you just have to put in the hours finding a server that has the sort of crowd you're looking for. The short answer is that you don't have to use voice comms, and that your experience of the game will depend on the people in your squad
For me, I miss the simplicity of RO/DH, when you could just pick a side, pick a role and get on with it and team-play or lone-wolf depending on how you felt. I understand that these Project Reality descendants are all about making game-play more realistic and less run-and-gun, but I resent being forced into it.
I was lucky last night in that I joined a squad with my son (I say "lucky" - must have done some good parenting!) and some of his mates, so it was a "safe" environment in which to learn stuff (your squad's comms are isolated from the rest of the server and you can block people from joining it). That's the best way to experience these games - with people you already know
In the end, though, these MP games are a social thing (I got to virtually know quite a few people through DH and to know actual real people through MP flightsimming) and to get the best out of them, IMHO, you have to bite the bullet and join in that side of it.