Obviously, if you don't like the Guardian's centre-left outlook, and are unimpressed by its longstanding journalistic ethos, you'll probably not want to subscribe. But, as with all other UK-based Kindle newspapers, you can have a 14-day trial for free, via Amazon, and judge this version and/or the newspaper itself for youself.
To counter some negative reviews that I've read, be aware that with Amazon you probably shouldn't trial any Kindle subscription if you're using your Kindle as a "stand alone" device, say having bought one in a shop... you'll need to access your online Amazon account to cancel, which can be time-consuming and tricky to do via the Kindle's browser. That is not an issue particular to the Guardian; its an Amazon issue, and I think they need to ensure that you should have a simple "cancel subscription" option, equivalent to the "add to collection" feature when you right-navigate a book's title.
What you get is an advert-free equivalent of the print edition of the newspaper, which will be delivered by Amazon to your Kindle when the paper goes to press (so long as your Kindle can receive it). Like a newspaper, and unlike the Guardian's website, it does not update itself during the day. One advantage of that is that it's on your Kindle, like a book, so you don't need a wifi or mobile phone connection to read it. Having subscribed since last year, I've seen it improve in content and ease of navigation, and find myself able to flick through it to what I want to read first, then back to other items, as I'd do with the 'real' thing.
Personally, I've switched easily from buying the paper to this subscription, and find this format suits me. I like having a virtual morning-paper waiting on my Kindle when I get up, and being able to read it without having to carry a fresh bundle of dead tree around every day, which I'll then need to bin/recycle. The major down-side I've encountered is that you can't use it to wrap up broken glass, although I also sometimes miss having the crosswords to fill in (as far as I can) when I'm being bored.
To be topical, I'm also happy to pay £9.99/month to help ensure we continue to have the high-quality journalism this newspaper supports... as we're now finding out, if it wasn't for the Guardian, it's quite possible that NewsCorp would 100% own Sky, and the Murdochs, the media, the police and our politicians wouldn't be undergoing the scrutiny of the Leveson Inquiry.