In regards to walls, there was also sac pulling, ie. pull everything to the boss, with the healers and DPS doing nothing (so that they don't register on the enemies aggro list), letting the tank die, all mobs leave, revive the tank and continue on. There is also the less severe one of pulling to the boss and keeping the mobs by the door and pulling the boss. Once the barrier went up, it would lock enemies out whilst keeping you inside, again, skipping them all.

As for dungeon design in general, there are a few things they can do to spice it up. Add environmental hazards, going from memory, I don't think we've seen them since SB? Add mobs that need to be stunned/interrupted so that you need to pay attention. Maybe add field effects that enhances enemies/debuffs your party etc. Just that little extra could make a big difference in how dungeons feel.