Yoshi's Story is prob best example. 2D platformer by Nintendo with gorgeous graphics. However, it was a lackluster, forgettable game. Still it proves the 64 was more than capable of exceeding 2D experiences from SNES.
Other examples are StarCraft 64, Bust-a-Move 2, Mortal Kombat Trilogy, SimCity 2000, Killer Instinct Gold (character models 2D), Magical Tetris Challenge, Rampage 2, Ogre Battle 64, MK Mythologies: Sub Zero, Clay Fighter 63 1/2 (2D character models), South Park: Chef's Love Shack, Mischief Makers, etc etc
It was more than capable of exceeding SNES quality graphics on every metric. The RDP on the N64 already had to render 2D rasters that were pre-transformed from 3D projections by the signal processor chip.
Remove that 3D transformation step and allocate some RAM for buffer and you had a perfectly capable 2D platform.