I think PBS Kids’ Nature Cat is very underrated. It’s not exactly a masterpiece or anything, but it’s one of the very few modern cartoons that carry on the tradition of the slapstick-and-one-liner kind of humor inspired by Looney Tunes and such. I’m pretty sure it’s Flash animated (if not Toon Boom), but it’s far above average, using old school techniques like squash-and-stretch, smears, and multiples despite it’s low-budget limitations.
The characters are cute and funny, and it somehow makes it’s educational format fit into slapstick and learning about nature entertaining. It helps that I’ve always loved animals. And the songs are catchy too (it amuses me that punk rock iconography like spiked collars and mohawks are now acceptable in a Y-rated cartoon).
A bonus is that almost the entire main cast is made up of SNL cast members. (I don’t actually watch SNL all that much except for the political sketches, but it’s gotta count for something, right?) Kenan Thompson, a ‘90s-kid favorite no doubt, unfortunately left after the first season, but it’s still pretty cool that he was involved.