Spent three days with the iPad 2 and definitely found the screen was brighter and, in my case, had a colder colour temperature.
I ended up keeping my first-gen iPad in the end for a few reasons:
1. No backlight bleed. I love watching movies on the iPad at night and all three iPad 2 units that I had (the result of swaps) had very bad backlight bleeding.
2. I prefer the design over the new iPad. I don't have a very detailed rational but I just like the rounded back, speaker placement, and aethestic.
3. I have always believed that, in most cases, Apple tends to over-engineer first generation devices (big exception was Mac Air).