Firstly, if you haven't realised by now that going into a movie with very specific expectations based on a synopsis or trailer is a bad idea, I just don't know what to tell you. Reviews are hardly any more reliable but I'm going to try anyway....
Now we have that out of the way -
As others have mentioned, this isn't a rom com. It isn't really a comedy in general; there are genuinely humorous moments (think wry grin as opposed to outright laughter) but the film is not trying hard to be funny as its main objective. It's also not a sci-fi. The time machine essentially serves as a McGuffin, it facilitates the telling of the story but is not central to the actual message of the story. Pulp fiction was not about what is inside the briefcase, and this is not a movie about time travel. It's about emotional baggage, mental health, love and the futility of trying to force someone else to change.
This is one of the better movies I've seen in quite a while. The acting, dialogue and cinematography are great. The plot is smart without trying too hard (Christopher Nolan, I'm looking at you) and deftly tackles some moderately dark subject matter in a tasteful and realistic way.
I hope I've convinced you to give it a try. If not, I'll come back tomorrow and perhaps then it'll work...