I downloaded Duke Nukem 3D on t'Xbox the other day, and have been playing it much of late. I did have the Saturn version way back when, but used the level select to skip through any bits I found too hard (i.e. most of it). So this is more or less a first playthrough.
And you know what's interesting? Its astonishing cheapness.
It's pretty hard, yeah. But a whole bunch of its hardness is due to the developers being cheating scumbags. Enemies fly around, shooting at you from slightly higher than you can move Duke's line-of-sight. Crucial bits of level-progression stuff are hidden in scenery that is nearly impossible to discern from non-descript background art. I've just come across a new type of enemy that flies at you and then self-destructs, doing a ton of damage - it's the aneurysm-inducing suicide soldiers from Serious Sam, except they can come from any angle and they're almost silent.
I'm not disparaging the game as a whole, mind. It's still a lot of fun to play, and it's interesting seeing the sort of stuff that became FPS standards: if I remember right, it was the first in the genre to offer some real-world environments; there are some basic switch puzzles that presage the way the genre has gradually grown a few brain cells; there's an emphasis on inventive weaponry, some of which is still distinctive (Shrinker! Woo!), as well as early outings for the sort of trap weaponry that is now common.
But it really is remarkable to see the sort of shenanigans that we used to put up with. Gearbox won't be able to get away with putting this sort of stuff in the forthcoming Forever. (If it actually is forthcoming. I'm remaining sceptical and Scully-like until the boxes are on shop shelves.)