I will admit that at first the CG version looked kinda weird and washed-out to my eyes, because of all the extra effects, but other than that the increase in detail and how much smoother it was blew me away, and I quickly got used to the extra effects/processing/filters/whatever (I'm not a graphics guy ) and think it gives it a more realistic look.
I haven't played the LG version in a couple years now (in fact, I sold off my 360 copy), and at the time I thought it looked amazing (aside from some PS2-quality ground textures), but after growing accustomed to the XB1 version, it probably looks like sh*t now.
Not to go too off-topic, but I kinda had a similar experience with Assassin's Creed. I first played Black Flag on 360 and thought it looked incredible, then I played through it on XB1 just recently and while I noticed all the nice new effects, the graphical upgrade wasn't that noticeable to me at first. Then I moved on to Rogue (the next chronological game, historically speaking) and whoa, the difference between XB1 Black Flag's graphics and Rogue's 360 graphics was much starker than I would have thought (and since Rogue is basically Black Flag: Seven Years War Edition, I think it's a fair comparison). So many little details I'd taken for granted in the XB1 version were missing, the framerate wasn't as nice, and the shadows and draw distance looked much worse. I've gotten used to it now to where it looks fine, but at first it was pretty distracting. (BTW, can we get remasters for Rogue, III and Liberation, Ubi? Pretty please?) My point is, I imagine it'd be the exact same thing if I were to play the 360 version of GTA V again, after growing so used to the XB1 version.
That said, the LG version pushed the 360 and PS3 to their limits and I'm kind of impressed they got as much as they did out of them.