I played TW1 after TW2 and yet didn't feel like it controlled badly at all. In-fact quite the opposite, many elements of TW1 feel much better (Especially in the Control/UI/Inventory department) compared to 2.
Although that said, I'm someone who has always gone back and played older games (Especially RPG's) and so older Graphics, Controls, UI's etc, never really shock me at all and I tend to transition very well. Perhaps if all you ever play is stuff like Assassin's Creed, Modern Shooters, Rockstar Games etc, then even something that really isn't that old like The Witcher 1 might still feel a little odd.
The Graphics have certainly aged, but the Artstyle is quite simply
fucking gorgeous and it's one of few games where the use of color is absolutely flawless, giving off this extremely natural, organic look, whilst simultaneously providing atmosphere.
I did a playthrough about 3-4 months ago when I got my 4K Monitor, and the game is still just absolutely stunning. (Saturation/Contrast might come up a little odd on some screens, my 4K Monitor isn't quite as finely tuned as some monitors)
http://abload.de/img/12315673krd17.jpg
http://abload.de/img/68678678eqclu.jpg
http://abload.de/img/23423423421mdks.jpg
Really the only elements about TW1 which do bug me a little (But definitely won't stop you from enjoying the game) is NPC Variation, Facial Expressions and Animations. There's like 10 random NPC models in the game just copy-pasted everywhere, and even some fairly major characters have the same model as 20 other NPC's walking around Vizima, it's a little weird.
Facial Expressions are basically non-existent and characters are very limited in the animation department when it comes to dialogue exchanges. The writing in the game is still absolutely superb, and being that the game was CDPR's first and it's a little old, you have to just kind of look past those janky dialogue elements and just focus on the quality of the writing.
I believe the Rise of the White Wolf Mod has improved textures in general, and there's a few graphical mods but nothing that does anything major. I either play it Vanilla or FCR and it definitely holds up, it's still a wonderful game.