RF4 is okay, but not spectacular. The only thing I was disappointed by was the cast, which was largely quite forgettable. Aside from that the gameplay has only improved, and there's a ton of content in there.
There's no yuri at all, not even subtext, and if you select the female protagonist you're locked in to romancing guys (and vice versa). Like Mochinochi said, you can change your appearance after a certain point, but functionally the game treats you as what you started the game as.
All in all, it's a decent entry in the series, but you wouldn't be missing out on much if you skipped it. I'd hold off for RF5 now that we finally know it exists.