Rosario to Vampire... I don't believe I've ever encountered a series quite like you before. That is not to say that the plotline is unique, or that the characters are original. I meant it as in I don't believe I;ve ever seen such a technically average series before, that I ended up liking so much.
Story: 3 out of 10
Despite me thoroughly enjoying the first season of Rosario to Vampire - and happy to start the second soon - Rosario to Vampire follows an over-used, average storyline that has been used by countless other harem comedies. A human boy ends up in a school of monsters, and along the way, he picks up a bunch of super attractive females who somehow find his average everything attractive.
There are tons of annoying scenes in the series, such as EVERY time Moka changes into her vampire mode, there is a 30 second dialogue that gets super annoying. Also in the vein of bad Harem comedy, Tsukune ALMOST kisses a girl every episode, but something always gets in the way.
Animation: 5 out of 10
The animation for Rosario could only be described as "average". Character design is fairly well targeted at teen males, and heavily relying on the typical harem attributes, ie. hair antennae, large gyrating breasts, panty shots, and sparkly backgrounds during "intimate" scenes.
Sound: 5 out of 10
Much the same as animation, sound is just average. No music is particularly spot-on, or inappropriate. It takes the backseat for most of the series. The voice-acting is alright, all the females have very attractive voices, and perhaps one of my favorite scenes of the show are the noises made during the bloodsucking scenes at the end of most episodes. "Kapuchuuuuuu".
Characters: 6 out of 10
This was a particularly difficult section to judge for me, because I loved the characters so much. Unfortunately, when you take s look at them technically, they are nothing but baked pieces of dough fresh from a cookie cutter. Be it the loving sweetheart, the perverted temptress, the loli witch, the goofy shy one, or the goth, all the females have typical personalities. And Tsukune is the definition of lead-male Harem archetype. He is awkward, untalented, and bland.
Overall: 6 out of 10
Overall, Rosario to Vampire is series that will only be enjoyed by those who are looking for exactly what it is: a light-hearted romance, with small amounts of humor sprinkled in. If you are looking for a Harem series, that has actual romance, drama, and comedy in it, I would suggest titles such as Shuffle! or Princess Lover, but if you just want something to casually pass the time, give this guy a chance.