Overall I thoroughly enjoyed Blood+. It has the perfect amounts of violence, plot development, character development, and don't forget romance!
Now for the let downs:
The first episode with the flashback is a bit misleading because the series in ALL blood and gore. The plot ca move a bit slowly at times and it is heavily dependant on a main character that seems to just be completely useless at first, but it gets better towards the end. They also could have given a specific timeline a bit more because all of the characters have a lot of history. Some of the fights are kind of a let down and bit short in some cases.
Now for the awesomeness:
The animation is really all that detailed but it is quite good. And of course, all the characters are very well-developed and you can see the changes in their personality as the series progresses. The male characters (most of them anyway) are actually fairly attractive, which is always a plus for girls. Even though the series doesn't revolve around romace there is enough of it to make you happy. lol And of course, it isn't obscemely long or boring and it has enough comic relief to not make you depressed.