iPad with Retina display comes with an all-new Apple designed A6X chip, faster Wi-Fi and LTE performance, an all-new FaceTime HD camera, and the new Lightning connector that is all digital. iPad mini, on the other hand, has a fast A5 chip, FaceTime HD camera, a 7.9" display, etc. The price difference, starting at $499 for iPad with Retina display, and starting at $329 for iPad mini, it would be ideal to get iPad with Retina display if you need the amazing Retina display, and need it for 'serious' and productive uses. If you are on a budget, need iPad mini's portability and mobility, and still want a great device, go with iPad mini. I personally couldn't choose between either, and if you have the money, buy both. They both come in handy for different uses in the real world. But the decision is yours.
The iPad 4 has much more screen space and a better screen with higher resolution but the iPad mini is more portable and cheaper so it depends if you will take our everywhere play games and what your budget is. For movies I would say the iPad 4 for games iPad Mini. Please rate if this helps!