I was just having a nostalgic festive think back to the games I used to play on the Spectrum (and the Commodore at my friend's house). They were dreadful, of course, but suspension of disbelief made them amazingly brilliant and full of atmosphere.
Jet Set Willy - how many games these days can you find about a hungover millionaire tidying his house after a party? Very simplistic graphics but it was easy to feel that you were exploring a gloomy and magical mansion.
Ant Attack - Odd 3d game about a boy saving a girl (or vice-versa if you wanted, fair play to them) in an isometric ruined city populated by giant ants. It was set in some post-apocalyptic desert and somehow managed to feel like it. Also wins the prize for some of the most pretentious instructions in gaming history (which hint that the in-game characters are aware, Animal-Man-style, that you the gamer are controlling their destiny).
http://sandywhite.co.uk/fun/ants/AAInlay2.htmSaboteur - incredibly easy but who cares? You got to be a ninja assassin and go in a helicopter.
Thanatos - the parallax scrolling, as it was called, really gave this the required atmosphere. I remember dreaming about playing the game before I'd every actually played it, and when I bought it, the gameplay was exactly the same as my mind's version.
Castle Master - one of the first proper, solid-graphics, 3d First-person POV exploring game. I loved it but I knew it was the beginning of the end; home computers would have to up their game to do this kind of thing properly.