I also don't like when a show mixes genres at intervals. I recently finished a series called Kamisama Dolls. It's story was fairly serious in nature involving fighting with giant robot dolls things amongst a few factions however quite often there will be episode where they go to the beach for a fun trip or a vacation or shopping. Happy slice'o life stuff and it just feels to me like its interrupting the main story and is unnecessary and actually kind of annoying. It doesn't need to be there nor does it add anything to the show and gives the series bad pacing.