Not really a top five of all time but notable mentions from my formative gaming years and taking in the different formats of cassette, 3 1⁄2-inch Floppy Disc and the early years of Hard Drives. Unreliable memories of the precise model details of the format I played them on so some guesswork.
The Great Escape - ZX Spectrum 48k/48K+ (1986)
Best Film License ever and felt so vast and detailed despite being within the confines of a POW camp.
Knight Tyme - ZX Spectrum 128K!! (1986)
Some budget games were a bit crap. This was better than most full price games and made full use of that 128K beast it ran on.
The Secret Of Monkey Island - Amiga 500 (1990)
Lucasfilms made some great adventure games including the Indiana Jones and The Last Crusade which was great. Loved Monkey Island though, ignore the special editions and remakes of later years. This was sensational.
Wings - Amiga 500 (1990)
Not sure there was any other game maker like Cinemaware. Beautiful highly stylized games which absolutely reeked of the period and style of their setting while still being good fun. See also It Came From The Desert.
Championship Manager 93 - Amiga 600 (1993)
Not the ultimate version but where it began for me, real players, real leagues and impossibly detailed. Dread to think how many hours went into playing it.
Also the game series that eventually prompted me to get my first housebrick sized external hard drive....a ton of solid, clunky metal and I think it held less than 40MB. Absolute game changer though.
I could do numerous lists for each computer and then more lists of five for 8, 16 and 32 bit consoles. And then another for early handhelds such as GameBoy and Sega GameGear. Wish I'd kept them all in a dusty loft somewhere!