Basically, the series is about four girls -- otaku Kanna, airheaded and innocent Tsukasa, smart and tsundere Kagami and the clumsy Miyuki. Not much happens (if you don't count the numerous references to other anime and manga) -- after a few episodes, there's this set pattern that gets repeated over and over with some small variations.
And still it's funny -- not laugh-aloud funny or bizarre like Azumanga Daioh, but funny in an otaku, in-joke manner. There's not much plot, though there are some recurring themes like Kanna's visit to the Animate, the doujinshi she reads (and that poor Tsukasa gets to read too), etcetera.
The ending of the episodes is put in the form of the 'Lucky Channel', where an 'idol' talks about what happened, together with a classmate of Kanna's. She fancies herself quite the star, though -- and she abuses her poor sidekick. This disintegrates completely as the series progresses.
It's been described as 'extremely otaku-centric', and that is indeed the case. It does poke fun at things like fanservice, lolicon and all that sort of stuff, in a rather light-hearted manner.
- Lots of injokes;
- Fast-paced and funny.
- Too in-crowd.
If you're a die-hard anime fan, then you'll like this one. If not, then chances are this series will merely irritate you. It has an extremely narrow appeal. For that, I will award it a 6.5.