Seriously? Four player coop in Half Life? Classes? This would just make it some sort of freakish amalgam of three very different genres. I'm not against some new additons, but what you're proposing would make in half life in name only.
Besides when talking about Left 4 Dead of Team Fortress 2 you also have to take into account that Valve has to pay for the dedicated servers and devote some time and manpower to the patches, DLCs updates etc.
The quintessential HL trait/experience is a continuous campaign that doesn't contain cutscenes with action spanning a continuous period of time as if the player is living within the game. That's it, there's nothing suggesting new elements could not be introduced. HL2 introduced an ability to lead small squads of AI resistance fighters, why not transform AI into human controlled?
The franchise has already brought forth games that allow us to play as otherwise tertiary characters such as Barney Calhoun and Adrian Shephard. Why not allow players to play as these characters, not individually in their own campaigns like in the past, but together in cooperation?
When I talk of class system, the characters would have more subtle specialties than a game like TF2, but a character like Adrian Shephard would understandably be a better combatant and be better with typical weapons while Gordon with his suit would be needed to get the group through hazards, etc.
Sorry, but a game like that would
destroy a boring rehash of what we've already had with HL1 and HL2. I hope you're not against such an idea because you have no friends so you're terrified of a game built around sharing an experience with friends, that would be tragically sad if true.
Isn't counterstrike a Mod for Half Life? Thus, counterstrike players should all be counted as Half Life players?
Yes, CS's origins were as a HL mod, however like with many things involved with Valve the game became its own entity separate of HL.
No. Counter Strike: Source was always a separate game from Half Life 2.
Maybe in terms of functionality, however I think he meant that many packages of HL2 included CS:S. My original retail copy of HL2 came with CS:S.