Problem with Slime Pits, and there are a couple levels like this, is that every monster type with the exception of one is absolutely nasty and cannot be used as level-up fodder. In Slime Pits, that monster is the Meat Man. This makes the level far more luck-based. Don't find appropriately-leveled meatmen in early exploration? Restart, because you're going to expend too many tiles seeking them out.
Keep in mind guys that Slime Pits is a hard level, not a vicious level. It should be readily beatable to a veteran packing good preparations. As far as hard levels go, it's actually one of the tougher of the pack. I'd say Magma Mines is probably the only hard level that's more difficult (notwithstanding any changes that have been made this version).
Speaking of "hard" levels, if you keep decreasing the difficulty of Rock Garden you should probably knock it down to "normal" difficulty. Currently if you can find Binlor early in exploration, Rock Garden is one of the easiest levels on the board, and with proper preparations it's not particularly difficult even without Binlor. Now you're adding item drops to the plants? I'll have to play it, but if this is a substantial reduction in difficulty I'm going to advise reclassifying it as "normal" difficulty.