I played Star Fox Zero at E3 and the core gameplay was solid. Very very good. The problem was that the levels were pretty empty but if I recall there were visual improvements in the last Nintendo Direct and the games half year delay is bound to polish everything up.
I don't think there's any reason to worry about Star Fox, a Miyamoto and Platinum collaboration can't be dull, it's just maths.
Based of What I've seen in gameplay of both games, Star Fox looked very boring to me whilst the co-op federation force missions on the Treehouse actually looked fun. This is me judging off of gameplay. I'm sure Star Fox actually is fun but when comparing the look of the gameplay, I was surprised Federation Force was still met with such hate.