Well... I think it's... very much like the old one.
The look and feel has been changed a little, but not enough to make me feel uncomfortable with it, and also not enough to say it's a huge improvement. So
Look and feel : Still very good, +1 on the old one.
Size of download : Chunkier, so -2 on that. I liked the fact that firefox 2 was still small and lightweight. Firefox 3 is almost 8mb.
Ease of installation : Very easy... Just as any normal windows application. +0 (the old firefox was just as easy)
Ease of porting from old Firefox : Very easy... +2 (technically porting from the old Firefox is so easy you don't have to do it... but it gets +2 brownie points for getting all my addons for Firefox 3 (those that weren't compatible already)
So quick review...
+3 vs Firefox 2.
+8 (it should be a horizontal 8) vs IE.