My favorite thing about Helltaker might be that all the girls are, um, flawed. Because they are actual demons. Even the secretary. Dat ending twist. And even Justice (weird name for a demon) seems pretty okay with you getting eviscerated if it'll be "awesome", even if she won't directly kill you for doing or saying the wrong thing.
My least favorite thing is the gameplay switch-up at the end - and it's the only part you miss content by skipping!
Seconding TLS rec.