They're all playable, but the visual barrier is pretty high. I'd mention Morrowind as one of your stated examples. While that title still is playable, the low-poly models and terrain along with the fairly muddy vanilla texture make for difficult immersion. What doesn't help is the omission of the compass or of map markers. I don't mind not having fast travel as an option, but I absolutely need a detailed map to get my bearings.
As for Deus Ex; I'd consider it as playable, but you have to remember that the stealth, hacking and combat mechanics all feel a bit rough, compared to what we have available nowadays. They were cutting-edge back when it first came out and it was justifiably called the game of the year by some - but obsolescence waits for even the most celebrated of titles.
Then there's KotOR. It's a BioWare Star Wars RPG. You should not need more encouragement. *steals Peter Lorre's voice for a sec*
"You buy now, yes? You buy now, yes?"