It was decent, at least worth the watch if you have nothing better to do. And don't kid yourself, you don't.
I'm a big Hunter S. Thompson fan (how could you not be?), and I was rather surprised that this novel was adapted to film much less made into a nation-wide release starring Johnny Depp. I believe the book took a long time to even find a publisher in the first place. But yeah, that's besides the point; it's a fun movie, but nothing groundbreaking.
Here's the exact review I'd write if I had any writing skills, which I clearly do not: http://www.mountainx.com/article/37007/The-Rum-Diary
... And if you haven't yet, do yourself a favor and watch 'Fear and Loathing in Las Vegas'. Right now, you insatiable motherfucker.