The current gaming landscape has seen many different individual works. Even within genres, the core voices of each game are distinct. However, this doesn't hold true for game series that iterate on their systems in smaller ways, creating games that each take steps forward but feel identical to the previous entry.
These series may have quality gameplay and solid franchise identities, but individual identities are muddled in the process, either homogenizing a series or making all but the latest entry obsolete. Looking at a cross-section of what gaming as a whole has to offer imparts some insight into the nature of iteration.