Green Lantern can be an intimidating thing to dive into, because it's been going non-stop for so long and there are so many characters and so much complex history. I think the interesting thing about John Stewart Green Lantern is that he's a comic book character who actually grows and changes over the years, and does so successfully. I know that sounds like a simple thing, but when you really think about it, major characters don't do that often in typical super hero comics.
To explain that a bit, when writers write Hal Jordan, they don't often write anything to advance Hal's character. It's more about the situation than the man in the situation. And that man doesn't really grow often. They like to keep him at a status quo. This is understandable, though. Take Peter Parker. Many people have expectations for him, and from what I've seen, most feel he's best when he's going to college, not married, working for the Daily Bugle, and living with Aunt May.
When people write John, I think they feel they have less expectations to live up to, and they have more breathing room to take John's character on a journey, and as such, some really big and unexpected things happen with him, and he changes (the exploding planet was one thing). The cool thing about John is you can do things like that with him and he works great in so many different situations, unlike many other characters. A good example is what they did with him on the Justice League cartoon, with his relationship with Hawk Girl and all that. Don't get me wrong, I love Hal Jordan, too (most of the time), but John Stewart Green Lantern is a really fresh alternative, and the Mosaic comic really shows that.
John Stewart is known for being an unconventional thinker, so that comic series is definitely not like typical super hero fair. It's a very artsy and philosophical story about a guy who is struggling to break out of the shadow and get from under the thumb of his mentor, who the mentor kind of views as his bitch, or as John says, "his child-man". And about a guy who is trying to make a successful society out of many strikingly different groups of people who are all in an alien environment, instead of just being about pounding super villains. The story is really weird, and it makes sense because John is slipping into madness, though there is nothing that overtly says that, or blatantly points it out. Though it is technically a super hero comic, many people feel it's more along the lines of what DC puts out on their Vertigo imprint, like Sandman, 100 Bullets, and all that.
Sorry. After I made the first post, I pulled out the comics and read a few of them and was surprised at what magic I have sitting idly in my closet.
Definitely recommend downloading this, or something. If it doesn't tickle your fancy at first, give it a chance. It's so odd it takes a bit of getting used to.