For example, Metal Slug 3. My steam stats show I used to play it for 100+ hours. Before they added easy mode via infinite continues, I was really enjoying the game. I had to learn how every enemy behaves, where the powerups would drop and plan strategies to beat bosses. Every day I would get a couple steps further into the game and I could have played it for years. There's a great satisfaction and getting better at something and seeing the results.
Then the change came and I completed the game in one afternoon. I didn't care about all the cool enemy setups on later levels, because I could just bomb them, die when I ran out of bombs and then bomb them again after I revive. There was no real challenge.
I never turned that game on after that. Easy mode has ruined it for me.