Which is more important when criticizing a sequel: its qualities as a sequel, or as its own thing?

Hello, my name is Brother Templar, and I am working on a comprehensive analysis, breakdown, and review of Bioshock Infinite, and there are a few things I need to sort out before the project truly begins, starting with some questions I would like to address.

This is the third game in the Bioshock series (four if we include Minerva’s Den as its own thing), so obviously my project will require comparing this game to the others, however, my problems with Infinite as it’s own project and as a Bioshock project are two VERY different beasts, each needing to be addressed if this project’s intention is to come to fruition. However, not long after realizing this, the following question came to me: which is more important, a sequel’s qualities as a sequel, or as its own project? Which should be emphasize? Which should be the leading argumen?