One common game-killing aspect for me is that, once you have won the league a few times, have your tactic, squad and a youth team of future stars, your inevitable success from that point on makes things too dull to continue . As well as being dull it just isn't realistic, as all good things come to an end. It should be almost inevitable that your empire will fall
One good feature might be to introduce a squad staleness rating. Was the avoidance of it not the main reason Sir Alex was such a genius? Was the way Daniel Levy doubled-down on it not the reason why the Pochettino era fell so flat? A new signing, especially if he had the right character, would increase squad freshness. As might the unexpected sale of a stalwart. Some players may be disappointed he was sold, but suddenly . . .there's an exciting air-of-the-unknown around the place, and the more ambitious and professional of your wonderkids may react positively to filling the huge void
Speaking of professionalism, how about recreating the way that high-quality-low-professionalism (Paul Pogba) players will be attracted to high wage clubs, and then, having guaranteed earnings of 100 million over the next 5 years, suddenly the genuine ambition they once had evaporates, and so they whinge and scratch their bums and generally promote an attitude which could quickly spread throughout the squad and be adopted by any number of once exciting younger players who spend their formative years surrounded by a coven of prima donnas as the new squad staleness rating flies through the roof - hypothetically speaking
And I'm sure there are many other ways to help facilitate the fall of the empire. I think it would improve the challenge of the long-term playthroughs (especially with a Daniel Levy-esq chairman) it would be more realistic and increase the RPG elements of the game
