Bastion is a hard game to summarize without spoiling what makes it so powerful. In few words, it has a deeply thought out story, and tells it in a very unique way. It's one of those few times when a game becomes much more then just another game, and ascends into an art form.
At it's core, the gameplay is that of an isometric action game. You will find different weapons throughout the game, which you will use to fight your way through stages in a linear fashion. Enemies and destroying stuff in the levels gives you money that you can use to upgrade your weapons, buy different tonics(which act as equippable accessories), and so on. Nothing particularly special here.
Exploration is very limited to non-existent, though there are many parts where you as the player decide how "the kid" takes care of the situation at hand. The different weapons all act and feel different enough to keep the gameplay flowing smooth, but this isn't a pure action game, as often times there will be a quiet segment where the enemies stop coming to make way for the storytelling.
Throughout the gameplay, an announcer(we find out who he is and who he is talking to later) tells the tale. Once again, I don't want to spoil too much, but let's just say it's a clever use of 2nd person storytelling, both during the events and from future/past tense.
The game is a tad bit short, I clocked in finishing the main game at just under 7 hours. Once you finish it with an ending, the game unlocks New Game+, which lets you carry over your upgrades from the previous game. This also lets you play the game again with knowlege of how it ends, but as far as I can tell most of your choices don't really affect too much(the dialog is different, but there's enough story taking place around the main character where the main story events still all happen no matter what you've done). There is also a few side challenges, including some that only open in New Game+, so the game isn't one of those "you are done when you get the credits" kind of games.
This is a game where the story has taken center stage, to the point where gameplay will change or even stand aside entirely for telling the storyline. However, due to it's unique way of telling the story, you rarely ever lose control of your main hero. The story Bastion has to tell is a very deep one, and a lot is conveyed through the use of graphics, music, your own interactions, and the announcer all at once. This lends it some replayability as, like a good deep movie, you'll want to see it all again to fully grasp what is being told.
It's not a branching storyline until the very end, but because of the way it is written, those last two decisions and how hard they are for you to make will hit you on a very personal level, and it will truly feel like the entire weight of the world is on your shoulders when you decide what outcome you think is right. Once again I don't want to spoil how, but there isn't a "wrong" ending to Bastion. The ending you choose will not only affect how the game itself concludes it's story, but also tell a lot about yourself and what/who you believe in at the end of the story. That the game can make what is essentially a couple of 50/50 decisions with no true wrong answers be so deep is a true testament to it's carefully crafted storytelling and beautiful execution.
As an example of story taking center stage, I'd like to point out the inclusion of the "infinite continues" mode. In this mode, you literally cannot lose the game as you can just continue from where you fell or died. People who have problems with playing action games can still get the awesome storyline out of Bastion because of this, and it's a feature I think a lot of other story driven games should pick up on. The only thing this mode prevents you from enjoying is a few steam achievements(the ones based on not dying and not taking damage, for obvious reasons).
Parents should know a few things about the game before letting their kid buy it. First, the story is a deeply tragic one involving war, racism, and takes place in a world where even the "Gods" have shunned the people for what they have done(in real and powerful ways). There are the tonics which basically reference using the gameworld equivilent of alcoholic drinks to boost your stats. Last, there is a bit of in context swearing throughout the storyline.
As for violence, thanks to it's anime-ish look, Bastion doesn't contain anything too violent onscreen. There is minor amounts of blood, but once again it's existence is for story reasons, not just to put blood and gore in the game. ESRB says the game is E rated, with a warning for animated blood, violence, and use of alcohol. Personally, I'd say they got the rating right on the money for this one.
Control-wise, the game supports X-box 360 controllers and mouse and keyboard controls. I found with keyboard the lack of being able to press dodge and certain directions at once left a bit to be desired, but other players have played through the whole game quite fine with either setup. Both have been decently well thought out, and the game isn't particularly hard to the point of needing to be perfect with the controls, lending itself well to any controller setup.
If you have a non-xbox controller, you can use a third party 360 controller emulator to bridge the gap. Detailed instructions for doing this are on my Tips for Gamers page.
In conclusion, Bastion may not offer as much as the hit 50 dollar games have in content, but it comes very close. At 7-8 hours of play time, it sounds a bit short for all the hype it's been getting. But the reason for the hype is simple, this game is a shining example of good story telling through interactive media. With the story being the main focus and the game containing a mode that lets you play it with infinite continues(and thus any skill level), there really is no reason at all not to pick this one up and add it to your collection.
Perhaps the hardest decision about it is if you play games for story and quality, or for length and added time sinking fluff. If it's the latter, Bastion will probably seem like a waste of money to you. But if being told a good, solid story while being told how your actions are changing everything, this game is one of the highest quality stories to be found in video games.
The soundtrack is also a very good purchase. Once you play through the game, you'll probably want to buy it, but it's a full price album at 10 extra bucks. It's a fantastic listen, but honestly it's only really special because of the game and where the game uses some of the tracks in it's story. Not to say it sounds bad, quite the opposite, it's just it won't quite have the same emotional impact on someone who hasn't played the game. On the other hand, it's nice to have it available to buy to support the developers. It's your call, and you can always purchase it later after playing through the game.
You can play a demo of the game(which to me didn't really do the full game any justice), and also buy the game from it's steam page below. At $15 USD, it's 5 bucks more pricey then the usual "indie" game, but once you play it you'll still feel like you paid too little.
I highly recommend Bastion, it's easily become one of my favorite story games of all time, right up along with the Myst series of games. That is a title I am very picky about, and I'm proud to give that title to Bastion.