Thompson was a great writer, changing the landscape and parameters of journalistic writing and reporting as an art (not unlike Tom Wolfe; I'd categorize them together based on their impact). He gave to me, at a relatively early age, an open mind about viewing the world, acknowledging other views of the world and the desire to peek behind the curtain (and the curiosity to ask, "who put up that curtain anyhow").
Plus, he was funny as shit as well as smart, so a day spent reading one of this books was a day well spent.
I dare say you might mourn Jeff Tweedy's passing more than an anonymous tsunami victim (not imparting any difference of worth to either, but certainly they have different impacts on your own life). Similarly, having been touched and taught by HST, I mourn his loss, regardless of what he drank, what he shot up, who he boinked or how he left this world. Actually, it's even sadder to me to consider that sometimes those brains most vital are also most troubled.