The new notifications and notification screen are really nice. It's a combination of how WebOS and Android do it. There's a banner at the top which shows you the content of the alert like in WebOS, then there's a pull down notification screen like in Android to access the alerts later. This screen also has weather and stock widgets for your current location.
I really like iOS 5. It actually seems quicker on my 3GS than 4 was. The cloud features and wifi sync also work really well. Overall I'm impressed.
So I gave in and ordered the 4S. Ultimately I'm too invested in Apple's ecosystem (I want an iPad too) to switch to Android even if I am disappointed with the new features. I definitely wanted a bigger screen, a move away from the glass back, and at the very least HSPA+. But it simply wasn't worth it as I probably would have gone back at the next opportunity. Plus, I don't think I would have been able to continue having my work email on an Android phone as I don't think their security is strong enough for my work's IT policy. The nice thing is that AT&T moved up the upgrade dates for those who got the iPhone 4 last year to November so they'll only have to wait a month if they want to get the 4S at the fully discounted price. I'm hoping they will do the same again in a year.
If you have a 3GS or a 4, there's no pressing need to get the 4S with the way it runs iOS 5 though.