What I would do in that case is review them separately and then at the end say "Overall....." and give a general mini-review of it.
The final score is always derived from the entire mod. say oone part of the mod got a 9 and one got a 3. It would average out to 6. However if the good part was really good, or the lousy part really lousy, that score could go 1.5 points either way depending on how good/lousy each part is.
What I mean is if there's a really good part and a lousy part the good part of the mod would be the saving grace of the final score. I'd probably give the thing an overall of 8 and say "However I wouldn't waste my time with part B cause it really is not worth your time" or something.
Hope you understood all that