I frequently read that people at the time said the plastic minis in Nemesis can detract as much as they can add to the atmosphere, hiding important parts of the board space owing to their sheer size.
TI is often lambasted for taking an entire weekend.
Rosenberg's euro games are the bane of many a player trying to keep all possible actions in their mind.
Modern kickstarters can arrive in shipping crates worth of stuff, making you rent a lorry just to get your 25 minute party game to a meet-up.
What's your biggest regret purchase you can readily recall where a game was just "too much". No matter what specifically it was too much of.
For me personally, my big one was Android: Netrunner. I was excited to jump back into 2-player competitive deckbuilding after I quit Magic The Gathering early in the fourth edition. And it seemed so perfect. No luck involved, known spaces of cards, multiple factions, asymmetry which I nearly always love, it's all perfect!
On paper...
In reality I found out, yes, for me this is a strictly superior MtG. No downsides. Except that I'm no longer 16, and I no longer want to spend forever creating decks, collecting cards even if they're not random, or engage with sifting through hundreds or thousands of cards when working on decks. The exact things that made me excited to play MtG-but-better and brought me to buy Netrunner were the very things turning me away from it now.
Still got to sell it, oddly attached to my first-run box + all expansions now that it's no longer available. But played it like 6 times and that was it. 0 enjoyment. Gave actual MtG a try, even less enjoyment. Tried Keyforge, also even worse. I feel that the entire genre is just a goner for me, and I regret investing so much money into Netrunner. A lot.
I would put up expansions, in general, as being the bane of my collection. Specifically, I'd pick out the Factions expansion to Alien Frontiers as being a particularly good (bad?) example of this. The base game plays very well and feels well enough balanced. The extra rules, cards and ports added in the expansion just seem to over-complicate the game, and picking the right faction card seems to play heavily into winning.
I've had a similar experience with expansions, but feel it heavily depends on the game / on the expansion.
On the topic of over-complicating the game, oftentimes expansions expect you to have a good understanding of the base game and its core mechanics. The idea seems to then be "for all those people who loved the base game and played it for a long time, here's a new layer of complexity to keep you entertained for the next couple weeks/months/years". In other words, you'd only buy them if you are already very familiar and want more depth, more content, more mechanics.
However, sometimes expansions seem to significantly alter the core mechanics of a game that you've gotten used to and that you loved. Occasionally that can lead to a loss of mechanics that some players loved. If an expansion destroys the things I loved about a game, then of course I wouldn't like it.
Uh yeah I probably trailed off topic a bit, just wanted to share some thoughts on expansions.