This was my first adventure as DM. The biggest problem I had was with the Battle of Albridge. By the time the battle was set to start, the players had built it up, expecting a really cool battle and to hopefully finish off the Iron Circle.
I modified two of the encounters, threw one out, and added in a skill challenge to make the fight seem more epic. I drew out a map of where all the friendly forces were set up to show the players and kept them informed as to what was going on in the battle. First they had to go close a flank and save some soldiers that were being taken out by a group of tar devils, assassins, and an adept. Second, they had to defend a hill from an army of minions that had broken through (made a special hill map with special rules for fighting). After that they heard that the main bad guy was on the other side of the main battleground, so they had to do a special skill challenge to make it through the battle swiftly without losing healing surges. Lastly they fought the big bad, pretty much as the encounter is described (only on a different map, that same farm was getting tiring at that point).
It felt cheap to have him just run away, like what was the point of all that? So I had him escape but leave his horse behind. On his horse were maps and other documents that the players found useful (supply schedules, recruitment posters, various ideas for ways to get into the keep).
That was the biggest thing I changed. I played up Dar as a really cool guy, friend of the PCs, and hero of Harken. Then I put him with the PCs in the final confrontation with the teifling, who killed him right in front of the characters.