It's far better than Mermaid. It gets docked extra points than it normally would because it's replacing a much better ride. I'm mad as hell that is is such a replacement as well. But if you compare it against Mermaid, no contest that it beats the pants off of it. To me anyway.
The quality of Mermaid's scenery and its figures (outside of Ursula) are mostly cheap looking trash. The lighting is also horrible, and everything looks extremely plastic-y There's also a ton of exposed structural elements. Tiana has the decency to actually fill out its sets with detail from what i'm seeing. Even if they look empty without many characters.
Frozen is also still much worse. Again, a ton of that ride has blank vacant unpainted black walls and/or poor video projection. Very exposed ceiling structure again. Tiana's video projections of characters also suck, but there aren't quite as many of them by comparison as Frozen has. 90% of the ride is comprised of narrow empty corridors with barely anything in them. The ice even looks bad, just opaque painted flats instead of something that is transparent and refractive. And in Epcot's case, they also have those hideous face projections.