Size Comparison - iPad 2, iPad 1 and iPhone 4
iPad 2 is basically better in every physical aspect, thinner, smaller and lighter while improving performance of processor by 2x and graphics by almost 7 folds while still maintaining the 10 hour battery life.
Over all comparison - iPad 2 and iPad 1
iPad 2 is technically better on everything expect for the price since the iPad 1 is now $100 (P 4,000.00) cheaper. Being released on the same range of price of its predecessor, iPad (2) is still the most cost effective tablet in the market