Osamu Kobayashi's name has been attached to a number of anime series that AICN Anime has and will continue to tout as overlooked gems, including Beck, Gad Guard and Paradise Kiss. To say that episode four of Gurren Lagann is a drop and quality is to mistake a change in aesthetics for a break down in production. Everyone has their own tastes and preferences, and maybe Akai got sniffy in his dismissive response, but episode four marks the type of risk taking experimentation that anime needs to remain a vibrant form.
Kobayashi takes off the restrictor plate on the animation. Not that it was static and uninteresting before or after, but Kobayashi loosens the bindings on the characters and allows them to be more dynamic. He employs a technique which is like that of manga with concrete background and abstract characters. It's "cartoonishness" equates to a looser definition to the character models. There is more emotiveness and more willingness to relax the idealization. The individuality of the characters and the magnitude of their expressions become amplified. They don't look like they are coming straight off the design sheet in every frame, so they aren't as pretty as some might prefer, but, they are also less generic.