In MI1, there was a sense of questing as Guybrush Threepwood goes through training to become a swordfighter (the classic training trope like in Rocky and in martial arts movies), plus there was also the will-they-won't-they romantic tension with Elaine. MI1 was an origin story so it had the advantage of being able to use these well-loved tropes. Stan was a great character.

MI2 took it a little further with the unresolved tension with LeChuck.

MI3 didn't really have that same sense of tension or urgency because Guybrush is already in a relationship with Elaine and he's just trying to break the curse. MI3 (or CMI) was a great game, but it just didn't leave you wanting more.