I take this で as functioning like the English "about" or "with" and being more or less synonymous with (more formal) "において". This usage is pretty common, I think. Thus we find ample examples like this on the web such as:
"私達の対応で悪いところ・残念なところを教えてください。" "Please tell us about bad points and/or disappointing points about/with our response/treatment."
This で represents a relatively minor usage, which can be translated "at the point/stage", "at the time when", or "when in/at" (often with implicit contrast to some other points).
前回の微妙だった部分 unimpressive features of/in the previous (game)
前回で微妙だった部分 unimpressive features (existed) at the point of the previous (game)
Of course, in this case, the meaning ...