What games have you played over the years which were pretty good but only lasted in the moment and you look back now and think...damn I remember losing most of my weekend to that one...
I'll start it off - although the system I list maybe incorrect, I'll try and really dredge some obscure ones out..
Snowball - Text Adventure, Level 9 - Atari 800XL
Rainbow Walker - 3d Platformerish, Atari 800XL
Alternate Reality - RPG, Atari 800XL
Electra Glide - 3d Racer - really weird! Atari 800XL
Leather Goddess of Phobos - Text adventure. C64
Skooldaze - RPG? Spectrum
Little Computer People - God Game. C64
Mission Impossible - Text Adventure - Scott Adams, Spectrum
Phalanyx - 3d Shooter. Sega CD
Sherlock Holmes - On rails adventure?!? Sega CD