In Keep on the Shadowfell, there's two encounters in a hobgoblin barracks. The hobgoblins knew the party was coming, thanks to a bit of treachery, and so they were waiting. (I combined the two encounters into one and reduced the size a bit.) When the characters crossed a specific line, the hobgoblins dropped a portcullis and cut the party in half. Wizard and rogue on one side, cleric and fighter on the other. Then the hobgoblins ambushed the party from each side.
The wizard and rogue were on the ropes, facing a hobgoblin hexer and some of his warriors, and went down several times. I was certain it was going to be a TPK (I had a prisoner-escape plot lined up just in case) but they pulled out all the stops. The wizard had previously lit a hobgoblin bed on fire (it's kinda his thing) and they had shut the door on it, filling the room with greasy smoke. The rogue went back and darted in and out of concealment over and over, just barely staying alive (he had three hit points--then one!). He blinded one hobgoblin with some Kruthik poison they had previously harvested, and the wizard used "Ghost Sound" to lure him into a pit. Meanwhile, the fighter is going toe-to-toe with the hobgoblin commander and the cleric is desperately trying to keep everyone alive. Great fun.
As I look back, the best encounters have definitely been the ones with the most interesting terrain and player options. My players' eyes light up whenever they see a pit, and they've made a point of selecting forced movement powers. The climactic battle against Kalarel in the same adventure was not nearly as much fun--a bit of a grind, and it just didn't have a lot of interesting stuff on the battlefield.
The wizard and rogue were on the ropes, facing a hobgoblin hexer and some of his warriors, and went down several times. I was certain it was going to be a TPK (I had a prisoner-escape plot lined up just in case) but they pulled out all the stops. The wizard had previously lit a hobgoblin bed on fire (it's kinda his thing) and they had shut the door on it, filling the room with greasy smoke. The rogue went back and darted in and out of concealment over and over, just barely staying alive (he had three hit points--then one!). He blinded one hobgoblin with some Kruthik poison they had previously harvested, and the wizard used "Ghost Sound" to lure him into a pit. Meanwhile, the fighter is going toe-to-toe with the hobgoblin commander and the cleric is desperately trying to keep everyone alive. Great fun.
As I look back, the best encounters have definitely been the ones with the most interesting terrain and player options. My players' eyes light up whenever they see a pit, and they've made a point of selecting forced movement powers. The climactic battle against Kalarel in the same adventure was not nearly as much fun--a bit of a grind, and it just didn't have a lot of interesting stuff on the battlefield.