I've been an iPhone user since 2008 and I absolutely love the platform but when the iPhone 5 came out a lot of people said it wasn't a bit improvement. Well I upgraded from a 4S and its a nice step up. The main difference for me is weight and comfort in the hand. The 4 design was so slippery and the 5 totally addresses this with its aluminium backing. The speed bump is nice and the camera is also an improvement.
Also remember it has that pesky lightning cable, which at the beginning was frustrating but now I've got enough cables.
The Point: If you have a 4S then I would wait, if you have anything else then this is a must have purchase.