For me, it's Tyrian. It's an upward-scrolling, space flyer shooter game. The main attraction I have to the game is the endless possibilities for destruction. You have a wide selection of weapons (several different types for each of a front gun, rear gun, and left and right sidekick weapons or ships). The front and rear specifically have 11 levels of power. Some sidekicks require ammo (these are usually the more destructive kind), others have a theoretically limitless supply of shots. Even your ship's power generator and shields can be upgraded. Each level may depend on a certain goal of destroying an enemy within a certain time limit, or (in most cases) simply surviving the level to the end. Some ships, or some game modes will allow you to perform special moves to do anything from spitting out a unique weapon blast, to deflecting enemy fire, all the way to regenerating new armor on your ship. The music is distinctly 70s and 80s inspired Techno, and the sound effects were quite good for its time. I bought the game for the full $40 about 10 years ago, lo and behold it's now Abandonware and is available for complete & free download at http://www.classic-gaming.net/ But before that happened, it was entirely worth the $40 I'd spent. I got more play time out of that game than any game ever since. On the quicker machines of today, I have to run it inside a utility called DOSbox, which, as it turns out, is quite good at replicating the original experience (with an SB16 sound & FM music driver, like I had on the Pentium 133 I first played the game on!). Got any old DOS games you still have around that you want to play? Play 'em http://dosbox.sourceforge.net/ - and then post about it.