GoW - Eh, it's okay. The single player was the highlight for me, the multiplayer was just lame. That, and number 2 is right around the corner. (Maybe not for PC, but you didn't really specify which system.)
Frontlines - Played the demo for 360, it was actually pretty fun. Not really much I can say, never played the full thing.
Half Life: Episode 2 - Don't even really need to say anything, except this is the best game of all listed. If you've played the first ones in the series then this is a no brainer, but if you haven't then get them all and play them NAO!
F.E.A.R. Expansion - Depends on which one you're talking about... well, actually, no it doesn't. Both of the expansions are just an extension of the same-old-same-old that F.E.A.R. was. Nothing really worthy to warrant purchase of either.
Doom 3 - Eww, no, this game was horrible. The 'scariness' comes from the fact that you can't see shit and even though it's futuristic, mankind has yet to grasp the concept of integrating a flashlight with a gun. That and having to stop all the time for the stupid PDA system kinda ruins any suspense that was built. Note that all of the above mentioned things were improved upon in Quake 4, (flashlight on gun, no PDA system, etc.) so if you haven't played that I'd highly highly recommend that over Doom 3.
Gears of War (G.O.W): Mweh... G.O.W 2 is coming out... though if your in a shooter for story line... then yeah get it
Frontlines: Fuel of war: Havent played
Half life - Episode 2: Very fun just get the orange box
F.E.A.R Expansion: Because Repetition is more fun the second time around
Doom 3 - If you consider throwing money off a bridge... fun this is an improvement atleast... but then you might as well call hardcore mode in CoD4 realistic... and also add that rockets go straight
Seeing how your going after future shooters...
Fallout 3 seems quite good, also is a tactical pause RPG game if you want
And seeing how some are tactical
RSV2 is quite tactical (dare you to run in the middle of the map)
CoD4 Is a bit tactical... still feels arcadey...
