Honestly, I think the artwork hit its peak during the DPPt seasons; Ash in particular looked far more mature than he did in Unova - where he seemed to lose at least three years - and, whilst XY's artwork is fairly nice, it doesn't have the same aesthetic appeal to me that DPPt did.
As for the character designs...god, there are so many of them that it's difficult to have an overall impression, because they've gone over literally every design in the cliche book. If nothing else, designs are varied, and that's great - not everyone is stereotypically perfectly proportioned and pretty and, whilst I think they could stand to represent a few more ethnic groups a little more often, you can say that of pretty much any show, and it's better to just do these things occasionally than obnoxiously do them for the sake of doing them.
I would like more simple designs in prominent characters, though. Jasmine from GSC is one of my favourite character designs because she's plain and simple; she doesn't need outrageous hair or a costume to be memorable or appealing. Just a nice summer dress and straight brown hair. It makes her MORE memorable for it, honestly. A few more prominent characters like this every now and again would be great.