In most cases fan service feels like the obligatory sex scenes in hollywood movies. It sucks.
Don't mind the fan service if it's at least remotely funny or at least makes a tiny bit of sense, which it doesn't in most cases.
^This. I don't mind the occasional Marshmallow Hell or Accidental Pervert moment, but when a non-ecchi series starts relying on fanservice for most of its humor, it just cheapens the work as a whole. It feels like the author's desperate to draw in a demographic that wouldn't ordinarily read his/her work in a lazy (and futile) attempt to boost readership. I have nothing at all against ecchi manga, but if I want to read ecchi, I'm going to read ACTUAL ecchi, nothing else. There's a time and place for everything, and in my opinion, gratuitous fanservice has no place outside its own genre.