Sekirei and Kampfer are almost entirely unlike each other, except for the very broad conformance to the genre of "fanservice comedy"... and for one more thing: both had half-hearted endings for the season, which can serve as a springboard for sequels, if money is forthcoming (in case of Sekirei, this hope has already realized).
The dissimilarity of the two is actually rather striking. Perhaps I'm just approaching them from the position of a stereotypical hater: breasts? check! harem? check! So same! To be sure, there are some rather vague and high level similarities. The villains are in control in both settings, for one, and heroes rebel (some of them, anyway). Both series flirt uncomfortably with the SDB's "dead girl" classification. But just about every detail is different otherwise (e.g. Natsuru has the powers, while Minato does not, the slavery present or absent, etc.).
I like Kampfer's character art way more though. The Rushina factor is more sensible in it.