Tempest 2000 (Atari Jaguar)
I received this game alongside a Jag console, Cybermorph and AvP for Christmas '95. To be honest I knew hardly anything about it, except it scored 97% in GamesMaster magazine. I'm sure I didn't play it Xmas Day or Boxing Day as AvP stole the limelight, but I vividly remember firing up in my cold, dark, lonely room days later unprepared for what would happen next - an onslaught of colours, Melt-O-Vision (TM) graphics and techno tunes that left me spellbound. I played it regularly for the next 17 years until I finally sold off my Jag collection last Summer (sob).
I have never experienced the feeling of being 'in the zone' like I did with Tempest 2k, on one occasion I became so lost in the experience, in such a trance that I swear I felt like I was stood outside of my own body, watching myself from behind as I conquered web after web. Such an amazing, scary, unreproducible experience.
So yes, my greatest ever game is Tempest 2000!