The graphics still hold up - great character models, animations, lighting, texturing. Colour palette's a bit grey/brown dominated, but that's not rare in shooters.
I also like the use of Predator language and the HUD visuals. Takes a lot of cohones to record original sound for these creatures, rather than just ripping the effects straight from the films. Having the player's body rendered adds greatly to the role-playing factor. And the alien hive is probably still the most authentic-looking to date.
But. I'm immediately reminded why I can never bring myself to fully replay the game. It's pretty consoley in the worst way, with the quick-time-event glory kills, unfluid movement, focus jumping, small arsenal, limited options... And those glory kills do make me really uncomfortable. I don't want to jam wristblades into someone's eyes or impale someone arse-to-mouth, and I hate that I have to in order to play the game properly. I'd probably be okay with it if it just happened once or twice.
Also, it's strange to come back and look at those aliens now that we have Isolation. The rendering and animation is fantastic, but having them permanently crouched makes them look small. You don't feel the fear. The humans bug me too - not enough variety in faces or voice lines, and behaviour that just doesn't feel natural to me. I suppose it'd be hard to pick them off one by one if the marines all stuck together and formed firing lines, but perhaps this could be resolved by making Colonial Marine squads rare high-end opponents and have boggo security guards as the cannon fodder.
/Rant. There's a lot of good there, but a lot I don't like too. And thanks for doing these let's plays - it's good to hear your viewpoints on the subject. Also lets me appreciate parts of the game that I'd forgotten.