Rosario and Vampire season 1 (Rewatch) - 7/10
Well rewatched this a little earlier with one of my brothers. It's an enjoyable if lightweight watch, that unfortunately falls distinctly in the shadow of its much more heavyweight manga forebear.
Unfortunately, Rosario and Vampire suffered the same fate as many of Gonzo's later animes in that they toned the fanservice factor (although admittedly, especially in the earlier volumes there is a level of this in the manga), and skipped/jiggled around with the plot a lot.
The first season is tolerable in this regards, by and large, with a few edits and chronology changes, it does resemble the source material, unfortunately some of the best bits from the manga just don't transpire in the anime, and also the change in the ending distinctly weakened the follow on S2 which is largely fanservice/almost entirely non-canon.
Rosario and Vampire I feel can largely be recommended for its high class of incumbant seiyuu, Rie Kugiyama, Mizuki Nana and a few others, and because it makes a good stepping point to transist over to the far superior manga.
It is not an offensive series, unless you take dislike to the high fanservice levels, and treat it as what it is, which is a light supernatural harem show. The dissapointment being that it just doesn't really do the source material justice, but like many Gonzo anime's towards its final days suffered the same fate, so Rosario is not alone here.
Amongst the fanbase there is a hope that one day it'll get picked up for a Brotherhood style remake, the manga itself is still a strong seller and licensed in the west; and if you enjoy the series, I heartily recommend you check it out.
By and large, it is also more or less ignoring the S2 of the anime, or at least treating it as an alternate universe, and reviewing the first 3 volumes of the manga that comprise series 1 to take note of the changes in the material, and then enjoy the current ~17 additional volumes worth of material currently released for the series, as the first series of the anime really doesnt dig too deep into the material, covering a maximum of about 10 chapters of the current 90+