SPOILER ALERT : if you do not know the full story of the Lost Valley DLC, you should probably not read this.
I really liked the DLC overall and played over 60 hours ! Now that I know the story, what/who is behind the factions, I better understand some faction reputation drops and conflicts, BUT the way it is felt by the player during the gameplay needs some tweaking.
Here are two concrete suggestions (easy to implement I think) :
a) If one joins the Rebellion but actually slays their leader, you still lost all Forge reputation, though in reality you destroyed their leadership (trying not to spoil too much). It felt really bad, after doing all quests for the Forge, to suddenly drop to Animosity.
FIX : simply move that reputation drop to after speaking with the Rebellion leader, if the party did not kill the leader.
b) When doing one of the many quests leading to the secret base, even if your only quest is looking for a lost giant, you lose 100 Dominion reputation as soon as you are barely 15 feet on the map, and unseen by anyone. As this was a total surprise (I had not even seen the building yet), this was felt as very un-immersive and does not give the player much agency, even if there is a mild warning banter in the party. It seems the designer presumed the party would always be on a faction quest, but I went there rather early it would seem.
FIX : i) When a Dominion guard spots a character, give a clearer warning, similar to the one screamed by guards at forts and ii) trigger the reputation drop after a fight with the Dominion there. This both improves the immersion/role-play and makes sure the player really decides to start waging war against the Dominion.
As this requires only moving the triggers a bit further, it seems easy to implement and would greatly improve the experience.
Steam profile : https://steamcommunity.com/id/baraz/