The series is a lot like Working!!: a group of people together in a work-situation -- and it's never about the work itself. The difference is that these are all adults, which makes for a bit more mature plots. There is a slight problem with these relationship/situational comedies: they need to keep introducing new characters to keep things interesting. That's certainly a problem that Working!! had, but Servant x Service manages quite well without the need for new characters. That is because this series has actual plot development, instead of a perpetual status quo.
And it works really, really well. The series focusses on different (pairs of) characters and their relationships (sometimes merely working, sometimes also romantic), and that keeps it fresh and interesting to watch. The characters are all pretty sympathetic as well (though it takes some time to discover that with some characters), and that helps immensely.
And, let's not forget: the series is funny, without having to resort to that same-old, same-old ploy of "let's hit the male lead". It's just that the mannerisms and the peculiarities of the characters provide the comedy in a well-rounded way. I really liked the opening and closing songs and sequences too!
I really liked it: it's a great situational comedy that avoids the usual pitfalls. I'll give it an 8.