You guys really need to take
1) a chill pill.
2) Kornel's advice.
I was one of the main haters of AoB back in the day. You can do a search of my name to find me saying pretty much the same things. I think pretty much all newbies hit that wall, and getting over it is what makes them not newbies anymore. AoB is hard, no doubt of that, but if you understand the tactics it's possible and even fun.
If you don't have the patience for the videos, I can distill the main points for you.
1) Use bait. Oh lordy would you use bait. In AoB, your main threat for most of the game is shotgunners. They have one important weakness though; any color h (and I think the Bs, too) will, until it is very close or unless it is already standing on something it likes, approach an item on the ground to the exclusion of any other action. Blade, the top player of the game, pioneered this tactic, but I feel I made my own refinements to it that you can see in the video and my short discussion with Blade in the thread about how it worked. This and other tactics which require you to sit behind something may sound boring, but the tedium can be largely eliminated by remembering that run mode works with waiting, and it's very satisfying kicking in the door and cutting some fool to ribbons after he picks up the empty pistol you dropped for him. If you see a wad of hs in the middle of a big room, also remember that you can string them along with more than one piece so long as the FoV from one reaches the other.
2) Use corners, doorways, and other cover/chokepoints. Entering the line of sight of as few monsters as possible is key to your survival. Peek around a little to get a sense of what's around the next bend before you run in. If it's too much to handle, you'll be able to get back into cover before they hurt you, and you can approach from a different angle or just skip that group. This is especially important against the melee enemies; using cover can turn a pack of c or s of absolutely any size to a pile of XP at almost no risk once you have the chainsaw.
3) Shut the doors! This is especially important in "maze of rooms" and "lots of barrels" levels. This limits LoS, makes traps safer to use, prevents non-humanoids from wandering, and lets you know where wandering humanoids are since you can see on the map when a door opens. If you know the situation, you control it.
4) Close the distance. Don't be afraid to get in the fray. Basic foos shoot like storm troopers, all you need to take out up to three of them is to juke and jive your way up there. Imps and captains can be almost totally neutralized by running and green armor. With a level of HR and some blue, commandos, O, and B become your prey. The thing to remember is that with the exception of Mancubi and possibly Barons, enemies will not use their ranged attack when you're toe-to-toe with them, and the two exceptions are still pretty rare. If you can run fast enough to get to the center of a large group of enemies without taking too much, it doesn't matter what letter they are, you win.
5) Let c and s close the distance for you. These are faster than normal enemies. If you walk into their face, they'll get the first hit, sometimes the first two. Close until three-four squares separate you, then start strafing and backpedaling until they stumble into your reach. As Musashi said, cut them down strongly.
6) Use discretion. You need to kill most of the monsters. You do not need to kill all of the monsters. Killing everything gets you to about level ten in NTR, but you become a fearsome juggernaut at level six or seven. Distance is the main factor. Can you get to the middle of those seven O before they start burping at you? If not, let it slide. If you're fully stocked and the noises you're hearing are bigger than the XP you need, you can even skip most of a level without losing too much.