It isn't good. Certainly not when you compare it to The Times app. It is just an alternative way to view the website, rather then a way to read the newspaper on your iPad.
You have to scroll through articles, instead of seeing an article take up the whole screen.
Its poorly laid out
No original content that isn't available online
I guess if you are desperate to read The Guardian website it might be a better way to view it, but I certainly wouldn't pay for it as it just doesn't really give me anything that isn't already available for free. Its certainly not a paper in app form.
Seriously, review The Times app to see what a real newspaper app should look like. Its worlds above what The Guardian offer in terms of design and content (crosswords, The Times 5 days a week, plus The Sunday Times).