We're doing the Scepter Tower adventure right now, and I'm enjoying it quite a bit. I think that it was the perfect module for me to have chosen, given my goals - it does all the prep for the fights encounters for me, cool terrain and balanced monsters, and leaves all the rp stuff pretty much in potentia. There are lots of interesting NPCs briefly described but nothing to tell you exactly how to use them. Which means that I can do what I like with them.
Last night the group headed on over to the dragonborn Vannak's camp, since they'd deduced that he was the one holding the elf girl who'd recently seen the Lady. He wasn't adverse to a chat with the adventurers who'd cleaned out the ramparts, but seemed rather morose and low spirited. I added in an NPC of my own, a busybody uncle who wanted Vannak to go home already and stop messing about with this ridiculous quest to talk to a ghost. Some of their clan members had died on this stupid jaunt, and now they were dishonouring themselves with the kidnapping and (admittedly mild) torture of an innocent elf. The party members didn't do very well through the skill challenge and didn't get much out of Vannak in terms of information. Instead they ended up precipitating a quarrel between nephew and uncle. The uncle, having shamed Vannak in front of his men, further exerted his new power by handing the elf over to the party and the lot of them were more or less tossed out the camp.
The next day, it was all over Spellguard. Vannak had fallen on his sword. The remainder of his party was packing up to go home.
When I told the group this (I had an NPC come into Clewsoro's camp where they are staying and start gossiping about it) I could see on their faces that a) this was a surprise and b) they actually felt bad about it. I think getting your PCs to actually give a crap about an NPC deserves some kind of DMing gold star. It certainly felt good. Not to mention that we spent the whole first half of the session roleplaying and even my most hardcore hack n slash player seemed to enjoy himself. They had some bad rolls, but they were really smart about how they handled their situation, which is why I ended up letting them leave with the elf anyway.
I came into the Vannak encounter with hardly any notes. I had three or four ways that it could end, I knew all the NPC's motivations and goals, and I just kind of ran with it. I think that's where my biggest strength as a DM lies, in off the cuff improvisation. The risk that comes with that is the possibility that I might paint myself into a corner. Having the possible outcomes in mind throughout helped with that quite a bit.