Honestly, from the title, I expected something that gave actual 'insights' into the compiler, rather than the code. For example, indicating applied and potential (missed) optimizations. But seeing what it was, I was definitely not unpleasantly surprised :)

Being able to cut through abstraction is very nice and quite important when you want to understand WHAT you are writing from the machine's perspective (or even in general when you don't know the abstraction yet). I love using Haskell, but have no idea what kind of machine code GHC spits out at the end (something based on the spineless tagless G-machine, an abstraction I barely understand by itself).