well, we won't die without 2.2. 2.1 is quite a good update from 1.5 (better battery life, bluetooth etc.) but if I am not wrong, 2.2 supports stuff like wi-fi hotspots & tethering (older versions do it with apps), apps2sd (= able to install more apps!) and faster performance.
Or at least, these are the three reasons I have for wanting to upgrade to 2.2.
there's adobe flash support too, but not too important for me :P
Here are some of the highlights: Android 2.2 Platform Highlights | Android Developers
For more details...Google!