I don't find Planescape: Torment hard on the eyes, especially not with the widescreen mod. In general I tend to find 2D visuals age fairly well so long as they're capable of supporting higher resolutions. It's why I have little trouble playing a game like Baldur's Gate and even comparing it shamelessly to Dragon Age in terms of visuals:
Solid art direction is timeless.
What even I, an ardent 'classic' gamer who loves to dig into ye olden annals of ancient video gamey history find hard to bear however is early 3D or 2D games like Wolfenstein which pretend at being 3D when really they aren't. It's just really, really hard to bear especially when you're stuck at a low resolution because a higher one will cause the poor pixels to explode or somesuch. And claymation... why oh why did so many games in the mid to late 90's go with that claymation look? Eug.
Myth: The Fallen Lords was for the longest time one of my favourite games. Now... It's still fun to play actually, the gameplay mechanics are as solid as ever. But my god does it look miserable.
I still love the old series, but it certainly doesn't make it easy for me visually. I also have to agree with others mentioned games like Deus Ex and the like. Much as I love Thief, System Shock 2, Deus Ex and the like frankly they look like ass. Just doesn't age well. There are a rare few games which still look... tolerable. But for the most part? Terrible.
Makes me wonder what I'll think of Crysis and the like ten years from now? Hmmm....