HereForTheBeer: Same here, for the most part. The last chapter / area, in particular that final building, was what stopped me cold. I simply don't have the FPS chops these days to get through the ending on Normal, though everything up to that point was manageable.
These are different from the normal FPS action and get much harder if you brought the wrong weapons with you.
Bring these from the previous chapter:
OICW
Shotgun
Rocket launcher
M249 MG
First hall:
Keep the enemies at distance and kill the rocket launcher guy in the back of the hall. Use only the explosive ammunition of the OICW and the rocket launcher.
Second hall:
Shoot one OICW explosive to the farther pillar on the right, taking one of six guards down (if I remember correct). Go to the left and do it again. If you are skilled, you might succeed with explosives. Go directly to the desk and duck yourself, switch to shotgun and hit one guard each arriving from the right and left. Back to the center of the desk and reload. If Krieger stand on it, the shotgun will push him back. The remaining fight isn't difficult. Use OICW explosives or rockets to take the guards and Krieger down, you can cause likely the most damage if he comes to the desk. By ducking, Krieger will throw grenades on a low level and they will we stopped on the other side of the desk, causing no harm.
Weapons for volcano:
M249 MG
Rocket launcher
OICW
Sniper rifle
After opening the gate to the volcano, go directly back into the niche on the right (ducked) and sniped the trigen on the installations on the left. If you can do it with one headshot, you can also still care about the trigen left of the center of the satellite dish in the volcano. (You can also do it later.) Back into the niche. First rocket trigen arrives, either plug lead into its shoulder/upper body from the nice or slide to the left until you can see its temple. Four sniper shots take it down. Wait for rocket trigen 2 in the nice, use the MG to take it down. Sometimes rocket trigen 3 and 4 already show up. You can throw grenades to the left side of the gate and they will bounce to the position of the rocket trigens and damage their health, but keep in mind that the blast also can push them more to the left so they can spot you easier. After all four are down, care about the rifle/solder trigen 2 if you haven't already done that. Sneak out of the gate either ducked or crouching with the sniper rifle ready. There will be a soldier trigen on the installation on the right, it usually pauses before moving positions, a good opportunity to take care of it. If you now take your binoculars and look at the installations on the right, especially on its left side, there is a soldier trigen waiting, mostly covered by the wire fence from a stairway going from the center to the installation. A few sniper shots and it is history.
Now scan the area for enemies. Rocket trigens 5 and 6 might already be heading your way, if not, go down, take the rocket launcher (haven't tried other weapons) and aim at the opposite gate. This will make them curious and come out. Go back to the front of your gate and shoot rockets on the ground near the rocket trigens. They should arrive heavily weakened at your position, if you go down the other side while they get near you, they might not come up. Use the MG to finish them. It's possible to do this without losing any health. There is a healthkit in the opposite gate and the elevate switch which you have to use. You can now go up and to some positions of soldier trigens you silenced before and collect their ammo.
In the center, starting moving to the installations with many tanks, hear someone cough and retreat. Depending on what you have left, fire rockets and OICW explosives near the tanks and concrete (you can also scan the area with the nightvision). Hitting the lower part of the vertical tank between the two horizontal tanks seems especially useful in taking the guards behind them down. Hide behind the steel parts of the dish in the center for reloading. After you are out of this ammo, go to the installations on the left, lay down and use the sniper rifle to shoot into the arms of guards near the tanks (they cover the other body parts with a shield. After you are done with that, approach the installations with the tanks. If you have still grenades left, throw them over the tanks. Sneak around the stairs with the MG ready. It's possible that you already finished everybody. Then up the long stairs and get the job done.