Ixalan is a bipolar set- the flavor/creative is A+, the mechanical execution of the set has a ton of issues because the 4-way faction split was a bad idea and doesn't work in practice like they thought it would in theory.
Included in this article is MaRo ranking the sets he worked on. Top two are Innistrad and Ravnica: City of Guilds. Bottom is Battle for Zendikar. One oddly low set is Amonkhet. Ixalan is also very low.