The 1993 Genesis version of Battletoads comes to mind. The first three levels got a very nice visual makeover, but from them on the overhaul was much more simplistic in general and sometimes almost limited to the color palette rather than getting redrawn graphics.

Considering it was a game that filtered an overwhelming number of players literally around that third level mark makes it much more glaring.

Still, the half-assedness was obvious from the get go as the first stages' enemies were redrawn but the Toads' themselves were just awkwardly resized with small color tweaks.