The open ended jungle missions were amazingly awesome - atmospehere, weapon behavior, damage models - all top notch and played well on the 8800 GTS 320MB (the rig in my signature).
The game goes downhill for me when you get to the alien ship. Even that ship gets boring, although its cool the first few minutes in that environment.
Definitely pick the hardest difficulty setting, and pick your battles. Most enemies in the game wear at least body armor, so they are naturally damage resistant if you don't hit the head. CoD4 wasn't much different.
Low damage? Some tips:
1: It's important to remember to have 2 different weapons setup - use one with suppression for sniping (single shot / 2 shot bursts max). Suppressed deal much less damage in the game, but also are harder to spot. Fairly realistic. Keep one weapon unsuppressed, for Assaults, or just remove the silencer before big fights.
2: The shotgun is a joke - at the distance it becomes effective, it's much easier to just headshot. If you need to use it, make sure you select the narrow burst mode.
3. Pistols, without silencers, are amazing. Put the laser pointers on, and use them for close combat situations.
4. Later in the game you get two weapons that deal significantly more damage.
- The Rail Gun can head shot frag a PowerSuit, or kill a small alien. 2-3 shots can drop the giant flying aliens. It's very useful, and you get reloads in the toughest sequences.
- When you leave the alien ship and end up in the ice sequence - equip the Incenerating bullets vs the small Aliens - they seem to deal much more damage to them.
5. Some of the Alien sequences have constant respawn, unless you push forward and take the next objective. Learn to recognize them, so you save ammo.
