The reason a lot of people come off underwhelmed (especially immediately after beating the final mission) is mostly a result of three act structure. It’s got a first act (attack the moon, find the pyramid) it’s got a second act (prepare to attack the pyramid) and it even leads right up to the third act. Then after the big revelation it sort of just ends. Sure there’ll be more plot stuff later, but it goes from 90 to 0 in terms of narrative momentum. The actual revelation is pretty solid, finally moving forward the ‘main’ plot everyone’s been telling them to do. What it needed was an explosion or chase scene after the fact to leave a good, exciting last impression. And you can have a full story, then still leave room for the post-game. Forsaken had three acts, resolved the immediate problems, then started up a brand new arc whose repercussions we are still experiencing today.