Finding good pure puzzle games can be difficult. Many games contain relatively easy puzzles alongside other types of gameplay and so get tagged as "Puzzle", such as The Legend of Zelda series. In this list, I'm most interested in games that feature puzzles as the core gameplay mechanic without major diversions. I also don't consider most adventure games to be puzzle games. I won't include any spoilers aside from very a explanation of how the game is played, often part of the puzzle is learning how the game works. Even though I'm mostly focused in the puzzles, I'll discuss other aspects of the game too.
Baba Is You 10/10
You play as an animal creature on a 2D tile grid, and push around word blocks to change the rules that apply to that level so you can complete it. There are a lot of interesting interactions. The difficulty is strong and there's a lot of interesting puzzles. Early levels are designed well to avoid handholding, allowing the player to enjoy as much discovery as possible.
Stephen's Sausage Roll 10/10
The difficulty is unforgiving, requiring every level to be completed in a zone before the next can be unlocked. This is the most common criticism of the game, but I respect this decision to force players to overcome challenges.
English Country Breakfast 8/10
This is increpare's other good puzzle game, released before Stephen's Sausage Roll. Similar to that game, ECB forces the player to complete every level in a zone to complete it, but there is more flexibility allowed with branching unlocks. The puzzles are less elegant with a collection of specific gimmicks. Some of these gimmicks are very easy and some are very hard, so the game can feel inconsistent at times. Some zones didn't feel interesting at all, but others had some very good puzzles. The 3D can be disorienting and the camera follow might just suck, but I consider it to be part of the challenge.