This is my second Canon camera. Previously I have owned Olympus and Minolta cameras. I owned a t2i before this and used a t3i for weeks for testing purposes. I will try to cover most aspects of the new features and image quality. For testing purposes I used a Canon 17-40L lens.
Look and Feel:
Not much to say here for the look of the camera. Looks almost the exact same as the t2i, t3i. The battery grip and accessories all fit the same. One thing that is different from the t2i is the proximity sensor. On the t2i it was below the optical viewfinder and above the screen. On the t4i it is above the optical viewfinder. I use an eyecup(http://www.amazon.com/gp/product/B003Y06336)and it used to make the screen shut off on its own regularly on the t2i. This is a non issue for the t4i. There is also an added dedicated movie button in the power switch now.
Feel is a little different...