I think the 2D animation in Frontier is on par with say, Gurren Lagann, but clearly is not up to the quality of shows like Eureka Seven, Planetes, and Mushi-shi. It lacks even the consistency of quality of Haruhi Suzumiya. And while it has some character designs that I think are rather well done (Ranka, Sheryl, Alto, for instance), it also has some totally amateurish designs like Mikhail, Luca, and Leon. As a complete visual package, its nowhere close to Zero. However, I think its been exceptionally well directed, and the CG work is rather good.
The show is just flat out good, but I for one am a little disappointed that the standard if quality on the 2D animation isn't something being pushed for a franchise like Macross.