4 points: Quest for Glory 4
3 points: Quest for Glory 1 (Hero's Quest)
2 points: Quest for Glory 2
1 point: Dark Sun 1
I've briefly tried a bunch of the old classics and usually found them a bit hard to approach and also I have often had little patience to deal with the cumbersome UIs at the time and hence I've saved them for a later time when I can muster up the effort. Some others I've found quite easy to approach but ultimately on the boring side (for instance Arena, Daggerfall). In general I'm not a huge gamer compared to most people here but I'll still throw in my 5 cents.
I found Quest for Glory (starting with the EGA text parser version of QfG 1) and Dark Sun quite easy to get into and intuitive, even though I'm barely older than QfG 1. So even though I haven't played many games in the list at length, I think the easy approachability of QfG and Dark Sun (which lead me to play through them, rather than file them away for later after briefly trying them) is a strong point in their favor. I think Dark Sun should be quite easily approachable to people who've played the IE games, TOEE and/or Knights of the Chalice. As for QfG, I was surprised how easy I found to get into an EGA text parser adventure-rpg hybrid.
It's hard to pick a favorite between Quest for Glory 1 and 4 but ultimately I liked 4 a bit more. Cooler setting, great soundtrack, more spells to play with, also I think it has the most soul of all the games in the series (basically if it sang the blues, I would listen). QfG 1 comes next, as the game that established the basics of the series and has quite a bit of charm (athough the setting is vanilla but this kind of standard European fairy tale feeling also has its appeal). I liked QfG 2 a bit less but it's still really cool and I liked how you could get lost in the desert and die of dehydration there. Also I think the QfG games lost something when they got rid of the text parser, interacting with a text parser is more engaging and fun than just clicking on stuff. The ability to take your character all the way through 5 games is another really cool thing about QfG that is quite unique compared to most game series (I know some Gold Box games for example also let you do that but in general it's not a feature that shows up often). I'd like to see more QfG clones, something about this kind of rpg and adventure game hybrid really appeals to me (I've played Heroine's Quest and Quest for Infamy is on my to play list).
Regarding Dark Sun, the setting is cool, the combat system is fun and the start of the game and the last battle are very cool but a lot of the midgame suffers from trivial difficulty (if you make a party with mostly or all three class hybrids, but then again so few D&D games let me play Druid/Fighter/Psionicist or similar multiclass chars with no equipment restrictions, so why wouldn't I take the chance when I get it?), which lessens the combatfag appeal, so I'll give it one point. Also the soundtrack is great (if you have a decent MIDI setup to appreciate it at least).