They are pretty much the same in regards to the RPGness... The major differences are the setting and the combat.

Cyberpunk might be a little more in depth because V can have 3 different backstories, that add incredibly small changes to some dialogues where as The Witcher you're always the same Geralt.

I didn't really care for Cyberpunk at first. I stopped playing before the end of the opening chapter. After the DLC was released I gave it another shot and ended up loving it and spent hundreds of hours over multiple playthroughs. It could of been much better, but it was a good game and definitely brought back the spirit of GTA 4-5 for me.