Having run a wonderful RotRL game recently, my one suggestion for future designs is to consider having a multi-stage boss fight at the climax of each module. It can be done by the clever DM but it would be even more helpful if it were designed that way. Often bosses and even interesting sub-bosses are presented alone or maybe in a pair. Even CR +5 enemies are not much of a threat to an optimized band of 4-5 players who may have had the chance to recharge or recover and have effectively 4 actions per round vs 1.
For example, the fight with Nualia might be really epic of she had some or most of her minions all with her, instead of picking them off one by one through Thistletop. I'm an old timer, and my favorite series was the 1e Slavelords. Best boss fights ever!
I made the final assault on Karzoug's tower a staged progression, with reinforcements arriving every few rounds. It'd be nice to see AP's include those kind of guidelines and builds. (Forgive me if they have started doing so more recently and I was unaware.)
Karzoug himself would be more interesting not as a straight fight but in stages as well, in which you have to use different stategies or face different obstacles/powers just to get him down to a place he's actually vulnerable. I admit a little influence from WOW here, but hey, it makes sense. In my game the Paladin tanked him while the Torag cleric worked on breaking the Soul lens, so it kind of worked that way, but it could have been better.