Counter-Strike's super-popular and constantly-updated. So Valve could be forgiven for just endlessly patching and improving it, like an MMO. But that's boring . They could also do something a little more exciting. Valve's Doug Lombardi:
With Counter-Strike 2, there's a big question between, do we go start over from scratch and build a whole new game, do we do something that looks more like Team Fortress 2 that is rooted in the old game but has a ton of new stuff, or do we just sort of take everything that's new that we've released and put that out in a new box.
I think we're leaning more towards the two more radical places than just sort of rolling up the new box and re-skinning the box and putting out all the new stuff.