Devs themselves are always going on about how constrained they are by budget and time limitations. My dislike of MP being shoehorned into a SP game is that all the resources used to generate that MP (in terms of manpower, time, money) could have been spent on the SP. The SP component in such a game may well prove to be good, but how much better could it have been with those additional resources?
I don't understand why every game has to have MP. Some sort of co-op mode I can maybe understand, but the deathmatch et al stuff? Aren't there 20 million clones of that crap already you can play?