Don't feel bad, I had this problem too, and I'm a well seasoned METAL GEAR nut case from back in the day. And while MGS III unfucked most of the cluster fuck from MGS II, which to me is just pure shit, it's the very title that has single handedly ruined my taste for the franchise after MGS/MGS Twin Snakes. For having implemented so much into the control scheme, we're still too damn limited in what we can do as Snake.
**Point in case, there's really not much point in having to sneak around constantly if the first guard you come upon, you were able to slit his throat or choke him to death, then strip his dead body of his uniform, AND BE ABLE TO TAKE HIS AK-47! Even if the uniform was a bit tight/small or too big, Snake would be able to get closer to his targets and unsuspectingly kill them, and you should not have to look for weapons in boxes placed randomly throughout the game. You freckin' take it off the ppl you kill when the killin's done. Thus, Snake would just continue in this fashion depending on the area where whatever soliders in the differring uniforms were at. You'd basically Recon long enough to mimic their patterns, kill once or twice or an approximate fit, and then you more or less infiltrate right out in the open. Doing all the other Black Ops stuff when needed. The stealth aspect is okay, but like for what you're asking about, for a game that could've been phenomenal, it ended up {at least for me} being marginally "Cool" and easily forgetful. With the franchise going into the Card Game realm it can't be much brighter. I'd play MGS or MG 2: Solid Snake over MGS II or MGS III any day.
MERCENARY X99
And fuck sneaking through enemies, I would just go rambo on them and kill them all. The enemy AI is pretty stupid but it's fun to slay them all. Hahahah. The story and cutscenes were badass tho, the game was well worth it for those aspects alone.
