The comedy follows Gabriel White, who graduated at the top of the class at angel school and attends a human school on earth in pursuit of knowledge, but then gets engrossed in a web game and decides its too much trouble to go anywhere.
Whether or not you've seen the anime, Gabriel DropOut is definitely a manga worth trying if you're a fan of the CGDCT (cute girls doing cute things) and/or comedy genres. If you HAVE seen the anime and want more, then I'll tell you right now that the manga's quality is about the same as the anime and that should be enough to tell you it's worth reading.
Story: There really isn't one. Gabriel DropOut is a mostly episodic series about angels and demons and their everyday lives on Earth (and occasionally heaven or hell). There are occasions where new characters are introduced and the characters' relationships
and interactions do have a little bit of development, but nothing really major or dramatic.
Art: The art is great, it's pretty much everything it needs to be for this type of manga. It's very expressive and consistently of high quality.
Characters: The characters (and the cuteness and comedy that arise from their interactions) are obviously the main draw of Gabriel DropOut. Let me just say I absolutely LOVE the cast of Gabriel DropOut. They're probably my favorite set of characters from any CGDCT manga or anime. There's something to love about every one of the main four girls. While some people feel Satania is the clear best, I think a case could be made for any one of the main four as best girl. And I think any one of the main four characters WOULD be the best girl if you stuck her in an average series of the same genre.
Gabriel was my personal favorite, her lazy, sarcastic, and indifferent attitude was something I found both hilarious and sometimes relatable.
I definitely get why everyone loves Satania and I love her too. Seeing her attempts to be evil come back to bite her in the ass or be ridiculed by Gab or Raphi is arguably the driving force behind the humor in the manga. Some people may find her being "bullied" a bit mean-spirited, but I personally didn't. After all, she never seems to learn and constantly talks herself up in ways she can't possibly back up.
Vigne is the "straight man" of the group so to speak and the most well-behaved of the characters, something which gives her inner conflict since she's a demon and supposed to be evil. Her attempts to act more like a demon are often wholesomely adorable and hilarious.
Finally, there's Raphi, the least well-liked of the girls, but probably my second favorite. Her sadistic side and the way she bullies Satania seems to rub some people the wrong way, but the series would not be as funny without her (and I can't stress enough that the "bullying" is portrayed as completely non-serious slapstick comedy).
While all four characters stick somewhat to their tropes, I just found the comedy and character interactions within those tropes to be executed far better than most series in the slice-of-life/CGDCT genre. Basically, Gabriel DropOut isn't THAT unique, it just does what it does better than everyone else in its genre.
The side characters are great as well and their presence in the series isn't over or underutilized. Master and Machiko were my favorite side characters. The misunderstandings between them (being normal humans) and the main four girls (angels and demons) were consistently amusing.
Enjoyment: I obviously adore Gabriel DropOut. It's both a funny and relaxing read every time a new volume comes out and I hope we get as many chapters and volumes of this wonderful series as possible. It's something I can read to unwind and relieve stress and its mere existence makes me just a little bit happier.
And that's about it. Again, I highly recommend this to anyone who enjoys comedy, cute girls, and a relaxing, episodic slice-of-life manga. Not everyone will love it as much as I did, but I think it's worth a try for everyone and most will end up enjoying it much more than not.