Finished Limbo after it was sitting in my library for years and it was really emjoyable. I did not expect to like it as much as I did but the puzzles were all completely doable (
::: spoiler Tap for spoiler except that one with the minecart and the electric rail grr) :::
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Also played through Mouthwashing and was pleasantly disturbed. The lasst 20 minutes get a bit long in the teeth but overall a great experience.
If you kill a sentient being for pleasure against its will, there is nothing that could make it ethical.