The art is really all over the place, but some people really shine. I like Lucina and Chrom - their art looks super detailed and polished. Actually, most of the lords like Roy, Lyn, etc all look good. There was definitely extra effort put into these characters, and it shows.
The default cast of Anna, Alfonse and co. look good, as expected.
Most of the Birthright? characters look good too, like Hinoka, Sakura and Effie. I like the soft, rounded sort of style they have going with those characters. Good detail on them.
I like most of the pegasus knights, though imo the production values on their art are a little below the ones I listed. Palla is one of the better looking ones. Catria definitely feels a bit pervy but not thaaat bad I guess. I might be biased.
Some of the art is a miss though. I don't like the thick black lines + flat shaded colors of some of the characters, like Olivia, Raigh and that blonde axe guy. It looks super jarring after looking at the smooth gradients or careful shading of some of the other art styles.