It always fizzles in a dramatic sense, though. The hardest part is normally just after the start, and other than the micromanagement nightmare of actually running an expanding empire, the challenges in front of you actually DEcrease as the game goes on. There's no climax, nothing to build up to, no denoument. Just one more fight or turn identical to all the dozens or hudnreds that came before.
I VERY acutely remember in Medieval II where it had become inevitable I would win I was thinking "What the heck is the point of playing on? What do I get? There's nothing more to see, there's no final super mission, just busy work with no value and much pointlessness, all to get a 'well done' message and perhaps a few seconds of cinematic." I'd had misgivings before, but that was really the point where the series fell out of favour for me.
Gameplay wise it is poor, and I loathe to see poor things like that in otherwise well-made games. The campaign mode feels like a setting with no decent objective- they TRIED decent objectives with the first Medieval and failed totally. At least Rome had the 'destroy the Senate and take Rome' thing, which whilst was not all it could be it did at least feel like a decent endgame objective. They could have built on that for MII but they actually took it entirely away! Just hold a bunch of stuff; once you have taken 20 provinces you've taken 100. No good.
Games need an endgame. Look at the Civ series- in theory those games could go on forever but the point of them is that there is a definitive endgame to it.
Of course M2 was not helped by my aforementioned removal of AI opponents thing- the best times I had in Rome was pairing up with friends playing against AI Barbarian hordes. Couldn't do the equivalent in M2. What nonsense.