In my opinion it depends on the game. There are games focused around the collectibles like Banjo Kazooie, which obviously thrive off of having more things to collect and secrets to find. These also add to the world and let the player feel like they are exploring the world, and learning about the little details, providing them a more immersive and enjoyable experience. In games where collectibles aren't the main focus, but something on the side, collectibles are done well by tying them to the world and giving the player some recognition, some reward for finding them. Completing all 120 shrines in Breath of the Wild, while not necessary, gives you a special armour set that pays homage to the rest of the franchise. NieR:Automata has tons of side quests which aren't necessary to complete and, while not exactly collectibles, I'd argue they work in a similar fashion, where by completing them gives the player a deeper look into the world they are in, exposing details that might otherwise have been missed if not explored.
Then there are games where finding an item adds nothing to the experience, and you can skip the collectibles and miss nothing. The Assassin's Creed games show this well. I haven't played all of them, but in the ones I have played, you always got a house and could furnish it with paintings and whatnot, but this added nothing to the experience I had playing the game. There was no change in any dialogue, no reference to various levels of furnished my house got, it was just there, as something to do, which really left me feeling annoyed at the whole thing.
Collectibles are a subjective topic, but I think on the whole, most people can agree that if there is no thought or reason behind the collectibles, then they are bad. But put some thought into collectibles, and they will be enjoyed by at least some players of the game.
