Does it really matter if it looks like a PS3 or PS4 game? The gameplay, atmosphere, and art style is what makes Team Ico's games effective. Their games always have a stylized look to them. What kind of improvements are people expecting?
Visuals do matter. Better textures, more impressive amount of detail would be nice; something commensurate with the new hardware. It's not required, but of course it does matter, to answer your question.
SOTC was hugely hampered by its atrocious frame rate. And while the art direction was stunning, frame rate aside, the game's visuals were good for the time on a technical level. Not amazing but solid and not like something from PS1. Similarly, ideally, TLG would look like a true next-generation game and not a PS3.5 type thing. Looking like a PS3.5 thing is, sadly, a missed opportunity. However I totally agree that it's by no means fatal and can still result in an awesome game.
Don't get me wrong. Uncharted 2 remastered is still a very sweet game in 2016. To me it'd still be an excellent entry even in 2016. However, seeing what Uncharted 4 could do in its generational leap in visuals, as opposed to just a 1080p/texture/60fps bump of the remasters, is proof positive that true next-generation visuals still can make an important impact.