I ran the newest version of Caves of Chaos for 6 players this weekend. The party was made up of experienced players, 2 of them only 3.5 experience, the rest had played 2nd, 3rd, and 4th. The party was made up of 3 rogues, 1 fighter, 1 cleric and 1 warlock. The session was very well received by all.
There was trouble with the party from the start however. The fighter had the military background and decided to RP as if he was a high ranking military leader and of course the rest of the party was not interested in his commands (being a predomonatly rogue party). The party split with the dwarven fighter climbing the side of the hill and entering the hobgoblin lair alone while the rest of the party entered the goblin lair. Fortunately the party reformed in room 23 with the dwarf bashing in one door and then the rest of the party flanking from the rear. It was a slaughter. Fortunately the monsters are so nerfed at this point there were no other problems.
Because there were three rogues in the party and they were using their sneaking ability quite effectively it magnified the underpoweredness of the monsters. I did require the players to describe in great dramatic detail their action if I was going to give them advantage when facing goblins with 3 HP. I also gave each goblin a chance to notice them with a wisdom check but most of the time even with bonuses the checks could not beat the rogues hiding. I was able to use the goblins stealthy ability to their favor a number of times and gave the advantage for a few hits as well as dividing resources.