Half Life 2 actually uses Havok 1 not 2. It may sound bad BUT Havok 2 actually spawned from the collaboration of the creators of it and Valve as they kept improving Havok for use in Half Life 2. Basically Havok 2 = Havok 1 + advancements made to it for Half Life 2.
On the other hand, Half Life 2 is a game that was built to use the physics engine from the ground up, just cos someone will licence it for his game doesn’t mean he’s going to integrate it into it as well. Deus Ex 2 and Thief 3 use the same physics engine but it’s horribly integrated and is not impressive in the last. Doom 3 seems to have a decent physics engine too but all it ends up is let you push objects around and shoot tin cans since they haven’t bothered to make good use of it in actual gameplay.
And since we are talking about flying objects, that’s the simplest thing and doesn’t show the true quality of an engine at all to just see that. Also, Counter Strike: Source doesn’t use the engine fully either since it’s multiplayer and would take huge ammounts of bandwidth to fully use the physics. CS:S is just the tip of the iceberg that is the Source engine in all aspects, both graphics and physics as well as sound.
As for Half Life 2 not having much of a multiplayer, well, someone needs to learn how to download mods some of the most complex and unique games have been developed as mods for Half Life 1 and seeing as it’s the most popular engine for mods, HL2 is sure to follow on the same tradition and attract most of the talented modders as well so expect to see a lot more on it with that kind of power in their hands. A LOT of very promising projects with talented teams are already planned (and some have started creating artistic content while waiting for the SDK to develop them code wise as well)
FPS games have already been evolving and HL1 was the beginning of it. For some reason the other companies didn’t continue the evolution (apart from terms of gfx and such but not actual gameplay) but thankfully Half Life 2 is coming to show everyone how it’s done
On the other hand we have great upcoming games that mix the RPG genre with FPS like Vampire the Masquerade: Bloodlines (using the HL2 engine) and Bioshock (sort of a sequel to the amazing system shock 2 using a modified Unreal engine)
Another interesting FPS I’m looking forward to is S.T.A.L.K.E.R (sandbox style FPS/RPG), the earlier mentioned F.E.A.R (If it ends up as good as the early information make it be) and also Pariah (which looks more “ordinary” than the likes of Half Life 2, but nonetheless really good, something akin to Halo 2 I guess.). Battlefield 2 looks amazing as well. Team Fortress 2 might actually come in the not so distant future as well…
I guess my MUST have titles at the moment are Half Life 2 (it’s going to be top class and apart from that be kept fresh for years upon years upon years cos of mods just like the original), Vampire the Masquerade: Bloodlines (It’s going to show Deus Ex 2 how mixing FPS with RPG is really done) and Battlefield 2 (You can’t go wrong with multiplayer action like that)
That said, some of these choices are because I don’t know the quality of the other titles (Not HL2 though, that’s a must!). Bioshock for example could end up a better RPG/FPS hybrid than Vampire while Team Fortress 2 might actually arrive (I heard a certain something from a very reliable source from within the industry) and be a better choice than Battlefield 2.