Huge leap from the 4 (as it has Siri, 8mp camera, faster processor) but also miles better than the 4S then screen is fantastic, large, brighter. The A6 chip means Siri works better, it's instant and fast. Build quality feels finer than the 4S. Not light or cheap (not sure what phone other people have been using. This really is the finest Apple product I've owned. Anybody considering upgrading I will say it feels like the Ipad 1 to Ipad 2 update. People only think the 3GS to 4 was a big update due to retina for the first time and because they ditched the curve design. Personally I think Apple can stick to the current one for years to come as it's very good quality. So what I'd say is the Iphone 5 screen is miles better but all the smaller features will become apparent after using it for weeks like better battery life and the low light camera. I go back to build quality again and the 4S feels heavy, but cheap more plastic feel but the 5 feels more polished, brushed and sleek. The 4S is basically just the Iphone 4 but a few additions. I would genuinely advise upgrading as the better 8mp camera, faster chip and Siri will really make IOS6 much more pleasant than on the 4S. So to summarise if you like the IOS system, want a faster device with A6 than even the current Ipad then it's a must. Best Iphone yet.