Don’t get me wrong. Expansions can breath new life and expand the breadth of a game. That can be a good thing. But they can also bloat a game or just make it different, not better or more interesting.
Ignoring all the supplements and expansions that I ran into with D&D, my first poster child for expansions was Carcassonne which happens to be an example of the good and the bad of expansions. The first two expansions, Inns and Cathedrals and Traders and Builders, are great expansions that add a lot of interesting choices to the game. But things slowed down for my group with Princess and Dragon, as well as the Tower. By the time we hit the Catapult, we were expanded out.
And there were folks who wanted to always play with every expansion they had. That led to games that were literally three times as long as the vanilla game. And you had so many different rules to keep track of. I remember coming to really hate the King and Scout expansion during one of those games.
In the end, I actually got rid of the base game and all the expansions as well as some of the spinoffs. The only Carcassonne I kept was Hunters and Gatherers, along with The Castle. And over the course of many years, that’s all I’ve ever needed.
And that’s the crux of the matter. Expansions are only worth it if you are going to play the game enough to get the intellectual and monetary value out of them. And that’s why I’ve become meh to them on a whole. I have found I can get a lot of play out of a game before I need them.
(And if the argument is that the expansion fixes a game? Oh, that infuriates me. I heard that for both Thunderstone and Pillars of the Earth. I don’t want to buy a broken game and then spend more money to fix it. I don’t want to buy or play a broken game period. If it’s broken out of the gate, then it should have been fixed before it was printed.)
When it’s actually necessary and actually good, an expansion is great.