if you could have any themed dungeon level - what would your theme be? e.g nature - fighting druids, animals and rangers. Siege - attacking well laid out defensive positions. Water - all things aquatic. what would float your boat?
Goblinoids. especially bugbears....with maybe some ogres. ;p actually. Aberrations; aboleths, mindflayers, beholders, otyughs, rustmonsters, ettercaps....Aberrations some of my favourite monsters to run and so I reckon I'd like to fight them as well. An Aboleth could be vying for control of something or other VS. a flayer cult maybe VS. a beholder with the weaker but more numerous monsters as their minions. Luckily (?) the PCs' get caught in the middle of it.
Of the options you present, laying seige to a thoughtfully constructed and reactive defence would be the thing for me. Big rooms of mixed mobs are all very well, but relatively easy to pen in and fireball to death, while completely open areas are a straight test of fighting strength. I've just finished a great fight in Hickory Branch where I managed to disturb 2 or 3 mobs at once- orcs, gnolls and a couple of ogres just beyond the huge fallen pillar (that also appears outside the temple), and then the bunch of orc archers lined up down the ditch to the west. The fallen stone work meant that they had to go round to approach me, allowing me time to soften them up with arrows and could set up for flanking attacks. Being forced to react to threats without the option of 'artillery' or easy crowd-control (was 4th level so no fireball/ stinking cloud, and web/ grease of less use against widely spread foes) was a good challenge, especially as I'm still at a stage where one good critical can take down a PC. Otherwise, spellcasters with a tactical flavour: have to take cover from fireballs or similar while fighting off summoned monsters as a striker sneaks in or circles round to take out the enemy wizards. Monster mash is pretty cool, though the risk of being overwhelmed by summoned creatures from all sides means I have to resort to deadly first strikes against the priests, which seems too much like metagaming/ cheating to me...
Is it really meta-gaming if you know from in-character knowledge that you're trying to stop a cabal of priests from summoning a horde of devils? That would make the priests top of my target list, certainly.
I suppose maybe not- but then again defeating one of the few fights in the game where the enemy have something like the magical firepower I can deploy by killing off the enemy with sneak attacks before he knows I'm there feels like I'm robbing myself of some fun. But as it stands there's a bit *too* much summoning power going on!
I like the idea of an aberrations level. my favorite would be a level of renegade, druids, rangers and animals. Animals for the front line, rangers for ranged attack, spells and summed creatures to take out key threats. but i do like the idea of a mad beholder with a menagerie of aberrant minions
