Although tsuchinokoultimate got his post deleted before I could reply, I want to clear up one thing that he said..
The article he referred to does
NOT state there will be "almost no differences" between the PC and console.
The article states that the differences "won't be huge." But when you look at the exact quote from Marcin himself:
For PC, which in theory is infinitely scalable, you’ll be able to get more, but you have to invest. On the consoles, the difference will not be huge because they’re actually brand new PCs. So I think gamers on each platform will get an extremely good experience and they should be very satisfied with the quality."
It's possible that Marcin wasn't comparing the consoles to the PC, but the consoles to each other, ie the PS4 vs the Xbox One. Either way though, "won't be huge" obviously doesn't mean there won't be "almost no differences."
These are the differences I think will be between the PC and the console versions:
1) Resolution. PC won't be limited to 1080p, but be able to scale to much higher resolutions, including 4K support I'm betting..
2) Frame rate. PC will obviously be able to get much higher frame rates than the consoles, which will be limited to 30 FPS.
3) Draw distance. PC should have further draw distances than the consoles.
4) Textures. Texture detail has very little impact on GPU performance (provided you have enough VRAM), so I'm betting the consoles will have the texture quality set to a custom combination of high and very high. PCs will be able to run the game at the highest texture setting, either very high or ultra.
5) Shadows. Big differences here. Witcher 3 will likely have NVidia's PCSS which stands for percentage closer soft shadows. Consoles won't be able to run that as it's too intensive.
6) Lighting. I don't know what kind of lighting system the game will use, but since lighting is very GPU intensive, I'm betting that the consoles will get an appropriately scaled back solution.
7) Ambient occlusion. PCs will have access to HBAO+, by far the best and most accurate form of game ambient occlusion. Consoles will likely get either regular HBAO, or SSAO. Most likely HBAO.

Anti aliasing. Consoles will use FXAA, whilst PCs will have access to superior forms of AA that include MSAA and TXAA.
9) Loading times. Whilst there won't be any in game loading times, the initial load should be much faster on a PC.
10) Object and detail pop in. Object and detail pop in should be much less noticeable on PC, since PCs will have further draw distances due to greater amounts of RAM, VRAM, CPU and GPU horsepower.
11) PhysX. Witcher 3 is confirmed to use PhysX 3.x. This means that the PhysX in the game should run very well on the console's eight core CPU, but will be limited in scale. On the PC, the PhysX will have the option to be hardware accelerated, which will mean much more impressive and realistic looking PhysX effects.
12) 3D vision support. Witcher 3 might have 3D Vision support, which the consoles obviously won't have.
Whew! That's it off the top of my head!