It's more than just "Sex and the City with lesbians" - it provides viewers an in-depth dramatic at how lesbians live, how they handle relationships, etc.
Having seen the first four seasons, I declare that the series is filled with great acting (each lady acts as great as she looks), very rich writing, and believable storytelling.
The L Word is not just about lesbians - it also features bisexual women and members of other genders. Any viewer, male or female, will find lots of things that are so gay or so unusual to them.