Typically different flu viruses still cause largely the same disease: two weeks of misery if you're healthy, a not unreasonable risk of death if you're very young (i.e. an infant) or very old.
Typically. Not always. The 1918 flu was so devastating because, for whatever reason, it caused rapidly developing and often fatal pneumonia in 20-40 year old adults, which is very unusual. That's not to say that the current "avian flu" would do so, just to point out that just because most flus act in largely the same manner, it doesn't mean the odd virus can't crop up that causes a very different and potentially far more dangerous kind of influenza. And given that this virus has already demonstrated itself a killer...well, medical professionals have reason to be concerned. It's got a real possibility for causing a killer pandemic. And I know epidemiologists and microbiologists who are reasonably concerned over it.
But me personally...I'm not worried, not because I don't see the threat, but because it's not an imminent threat until, as I think I wrote earlier, it passes from person to person to person through the air. And it will likely do that eventually - it's just the nature of flu viruses to develop that ability. But until then, it's basically an exclusively zoonotic infection, and little more than something to keep a wary eye on for most non-medical people. I'm personally more concerned about the current mumps and measles epidemics in the US midwest...