Plus, Digimon's actually got a little something we like to call a PLOT! Not to mention, they usually try to do something different each time.
From the simple, almost parody-like first series to the first human death in 02, to the borderline psychotic Kurata in Digimon Savers (aka Data Squad), there's always something new, as far as the plot of Digimon goes. Sure it's cliche, but it makes up for it by throwing elements, such as parallel worlds, sci-fi themes, and Asian references (such as the Devas being based on creatures from the Chinese Zodiac) into the mix.
Plus, you actually see the Digimon change, based on how they are treated, both in personality and Evolution forms. No two Digimon of the same kind necessarily evolve into the same upgraded form. For example:
in 01, Agumon evolves into Greymon, and then MetalGreymon, while in Savers,
Plus, their personalities may be totally different, depending on how they're treated, to the point of possibly making partner Digimon into enemies.