PlayStation 4 Slim 500GB Console - Must Read Before you Buy
I have owned both the launch PS4 and the C-Chasy revised PS4, as well as the original X1 and the X1 Slim. For this review, I will only compare the PS4 Slim to the 2 previous PS4 SKUs (shiny left top and dull left top).
If you have owned one of the previous PS4s, the Slim is noticeably quieter when downoading games or playing games from the hard drive. When playing games from a disc, the drive noise is about the same as the C-Chasy PS4 (also about the same as the X1 drive noise). In terms of thermals, the launch PS4 was slightly cooler than the C-Chasy PS4 and the Slim is considerably cooler to the touch on the top of the unit than either of the previois versions. Where the C-Chasy model felt hot to the touch, the slim is just warm. On thermals and queitness, the slim is by far the best PS4 to date.
The slim also has some nice additions that weren't found in the previous models. For one, the HDD is easier to replace in the slim. Simply remove a small l-shaped plastic strip from the back corner and you can access the drive. It took me about 4 minutes to replace the drive and begin the SW update. Another nice touch is the see through light strip on the new DS4. I didn't think I would like this at all but afyer using the new controller it makes the once annoying light bar somewhat beneficial.
On a performance level, the slim is the same as all PS4s. That is, they all play the same games and there is no difference in graphics, loading, etc. The PS4 Pro should provide faster loading times and semi-improved graphics on non-4k displays. The PS4 Pro is primarily for those who have or are going to buy a 4K TV though.