I forgive almost every anime if they have endings that I don't like but I just can't get over the ending of Boku wa Tomodachi ga Sukunai till this day I'm still pissed about that. If not for that ending It would be a cool anime in my opinion.
For me to watch an anime I need to be interested in the plot, the animation also plays a major role when choosing what to watch, but in the end I would say the plot.