Huh... This is a bit tough with me, since I seem to already know how I'm going to feel about something beforehand and beyond...
With that said, believe it or not, the movies Grown Ups and That's My Boy kinda took me by surprised, since I did end up enjoying them in the long run... Granted, the formal had some slapstick humor I didn't find funny at all and the latter's first third of the movie was already leaving me with a bad taste in my mouth (with both movie's soundtracks keeping me from giving up on any of them outright), but the character dynamics in both got me invested in those movies to the point that I was rooting for whatever character Adam Sandler was playing in either of those movies... Will I ever re-watch those movies again the same way I re-watch, say, Happy Gilmore or You Don't Mess With The Zohan for example? Not really, but I don't regret wasting time watching either of those movies overall...
Other than that, the anime series Haganai: I Don't Have Many Friends surprised me with its "harem subversion", in that I didn't know it was a harem series until someone pointed it out to me... (Well, that and its second season reminding me it was a harem series, but I digress...)