CoD4 is a different type of game from Halo 3, they shouldn't be compared. (I know they're both FPSes but different types of FPSes)
How over-rated a game is should not be regarded as a property of the game, judge how good it is, not how disapointed you were because you thought it would be better/different, that's not the games fault, sure you can talk about how it was over-rated in your opinion but just don't say another game was better voerall because it did what you expected to.
The SP does have multiple paths, sure, multiple paths to one objective at once but still, if you need to take out the radio tower, you need to take out the damn radio tower, not take out the radio tower OR complete a different objective.
I'm all for realism in games but when it comes to multiplayer, you just have to accept that balance is more important; sure, you COULD have a silencer and a sight, but then there would esentially be no customisability, everyone would carry the max ammount of genades, frag and special, and have a silencer, scope and grip and whatever else on every gun, making it into simply, sniper vs machine gun vs shotgun, and no uniqueness beyond that.
You can't complain about using the same multiplayer modes as other games, those are THE modes, they are clearly the best, most popular and most balanced game modes, they work so they are used time and time again.
I'm sorry, but CS:S doesn't have a trademark on the realistic, modern day, FPS genre, they just did it the best so far. It not like they were massivly intuitive, making a game no one ever thought of, its got realistic gunsand player models (as in humans and real guns), its modern, it's a shooter, not exactly ground-breaking... (not that CS:S is bad or anything, I'm just saying it's such a general genre you can't say CS:S own it or anything.)
"They released the Orange Box as a whole package for a reason: no one in their right mind would pay $50 for any single part of the whole package. Portal and TF2 are great games but they aren't well rounded (Portal is low on content and all offline while TF2 is all online without a campaign), Ep. 1 sucked patootie and should even have been part of the package, and Ep. 2 is, once again, short, all offline, and nothing special.
The whole box, taken as a single achievement, is better than CoD4. Portal is more innovative than CoD4, Ep. 2 is more polished, TF2's online play is as good or better than CoD4's but as a single game mediocrity with the minimal amount of innovation to keep a series alive wins this year..."
So what if no one would buy a single part of the package, that would be why valve released it as a package, it doesn't matter that no one would buy them if they were individual games, they're not... They're sold in a package as you said so your point is completely invalid as your esentially critisising a situation that doesn't exist. If you ask me if bears can fly to the moon and I say no, you'd have to be an idiot you then yell at me, "LOL! of course they can't, why the hell do you think bears can fly to the moon?!"