How I tend to rate animes:
I never tend to rate any animes below a 2.5* even if I tend to drop the anime. The reason I drop it is mainly because I couldn't really get into the anime, but this doesn't mean that the anime never had potential to do well. Of course, since I do prefer some genres of animes more than others, there is always slight bias towards certain genres, but that doesn't mean that other genres aren't treated equally. Everything should be given a chance, but whether or not someone decides to continue is up to them.
2.5 - Either a dropped series because I couldn't get interested or the series/OVA doesn't leave a lasting impression. The story as well as other aspects were probably lacking.
3 - Series/OVA was average. It is something that you would forget after some time. Movies based off of a series are normally categorized under here normally because they didn't have much to do with the regular story.
3.5 - Series/OVA had some aspects that made it slightly better than average, but it still isn't necessarily too good to be rated anything higher than this.
4 - Series/OVA was better than average. The story is something you'll probably remember and the animation is better than average.
4.5 - Animes listed here were exceptional, but there may have been some qualities they were lacking to get another half a star. Although, these are still something you should really consider watching.
5 - Most of the anime put under this category were masterpieces. It steps outside of the boundaries from some regular clichéd anime, and it is sublime. The story is truly something amazing which is normally followed by some superb animation. I highly recommend that you watch things rated here.