If you lick plain MSG, it tastes bitter. Add it to something very sweet and it just tastes bizarre. Sprinkle it on fried chicken and it tastes like you just dumped chicken gravy on it and pumped up the taste. It really does mainly amplify flavors.

And while MSG tastes very wrong in sweets, sweets generally always taste better with a bit of salt. Salt is its own flavor and a flavor amplifier.

Plain MSG absolutely does not taste bitter. I just tried some (again) to confirm, it's not salty & not bitter. Just a strong flavor of its own.