Love them!
Especially the well made ones with character info, enemy types, designs, backstory, etc.
Instruction Manuals are a thing of the past though, probably cutting down on print costs since everything can be found online.
I do appreciate when modern games do a nice full fledged manual though. This can be seen in Shovel Knight - Excellent full color manual.
Another good example is Shantae Half Genie Hero that recently came out on the Switch. Nice full color manual full of illustrations, reminds me of the good old days of getting a game and reading the whole manual cover to cover on the way home.