The tone of "Girls" is somewhat dark, cynical humor. It is about four young women out of college a year or so. They live in New York City, but unlike the Sex and the City ladies, they are struggling financially and, overall, they aren't very happy people. There are Sex and the City posters in a lot of scenes, as if to remind you that you are NOT watching that show. Their jobs are deadend-ish in nature, or just plain nonexistent. They have lots of what looks like unsatisfying or awkward sex. There is an undercurrent of disillusionment and shattered dreams with all of the plot lines. Graduating from college and moving to New York City, isn't the world supposed to be your oyster? Since you still have youthful good looks, freedom, and income, shouldn't your 20s be the most fun part of your life? Maybe for some, but that's not how it works for a lot of people. For some folks, either men or women, the years immediately after college are when you find out that the world truly doesn't care about you, or that you don't have the talent to do what you wanted to do. It is when you grow apart from your college boyfriend or girlfriend and wake up one day to find that you have nobody of significant romantic interest in your life. It is when you find out that there are jobs out there that are horribly boring and unsatisfying.
I normally get annoyed by the excessive (and often boring and pointless) sex in HBO's original series, but it fits into this series just fine. This show centers around the trials and tribulations of young women in their early to mid 20s, and one problem that they all share is an unsatisfying sex life. Having been raised and gone through college with today's "hookup" culture, the men in their lives are lazy. They barely have to lift a finger to get laid and they don't need to be romantic to seduce a woman at all. They have sex and then somebody goes home right after. If you are looking for one big feature to distinguish this show from Sex and the City, I think that this portrayal of modern sex culture would be it. Sex and the City portrayed it as glamorous and empowering for women. This show (and I am not sure if this is intentional) portrays it somewhat the opposite. Hannah has been having sex with her partner, Adam, for a long time, but she barely even knows him. Marnie has a long time boyfriend, but she's not turned on by or in love with him. The relationships that these women have are shallow and unsatisfying.
The themes are interesting, and the writing is clever too. The one liners are usually funny. The hijinx are sufficiently wacky and unpredictable. If you have shared experiences with the characters in this show, then I think that you will "get" it, and that you will find it funny. If you haven't, then this show might not appeal to you. If you were turned off from the show by its marketing or because you didn't want to see another "Sex and the City", then I highly encourage you to give it a look. Especially if you feel that you can identify with some of the characters. As a 38 year old man, I still could, despite being older and, well, male. This show doesn't appear to be too popular, and that disappoints me, because I really want there to be a second season.