Half life 2 wasn't meant to be a realistic game. HL2 has all your arc-type weapons: melee, pistol, automatic assault rifle, shotgun, grenade, rocket launcher, etc, but valve put their own unique style to it. But the game has much more than just these weapons: the physics fighting with the gravity gun, puzzle solving with the gravity gun, the story that unfolded, and even the vehicles. This really set the game appart from your standard shooters, and why HL2 is going to be considered far greater in gameplay than this mod, because all this mod is your standard shooter, no unique-ness to it, besides the story.
I don't think this game was what HL2 should/meant have been. HL2 had its own unique stamp on it. After playing the mod a little bit when it came out, I really wasn't too impressed by it in terms of gameplay. And I would have been disappointed if valve had released this game: Which according to "Half Life: Raising the Bar", this was the direction they were going towards, but scrapped it to make it more sci-fi. And behold, the game got pretty good critical reception around the world.
I know we can't really say what would have transpired if the game turned out this way (whether it would have gotten such a good review vs a bad one), but just by comparison and Valve's game testing (which they do A LOT of to make sure their stuff is top-notch), the game was better going for the sci-fi side of things.
Like orph said, you should play more realistic shooters if your looking for realism. Some come to mind: Stalker series, Ghost Recon, CoD: MW2 (black ops included), even Day Of Defeat (WWII weapons are accurate) and couter strike (the prices ARE very accurate) are more realistic with their weapon models.
I am referring to HL1 with the HD pack by the way
But M4's in standard military issue (since your picking up these weapons from US marines) dont have 50 bullet clips :p. not too realistic. Also since when does a Gluon Gun exist? Or the Gause rifle, those aren't too realistic last I checked.
With regards to head bobbing: it makes me sick too if I play it too long with head bobbing, and it detracts from the game's gameplay, and other features, so if your focusing on that, your really missing what the games are trying to showing you. EG: in HL2:E2 looking at the huge vista of the Citadel blown up at the beginning of the game, but your focusing at the lack of detail on the gravity gun because its not being set down by the player because its heavy while your standing.