I've been playing Gleylancer and Death Duel on Genny the most, got them for Christmas from the wife.
Remember what I said about Death Duel in that Christmas thread of it being a stupidly fun shooter? Well, after playing it quite a bit I must say that it's much more than that. In the game, you control a Mech and have to fight against monsters and other Mechs from a first-person perspective in an arena setting. Each opponent needs a certain strategy and set of weapons (you can carry three of them at the same time) to defeat. Some are very quick, some have high firepower, for others you have to blast off their limbs and weapons in a fixed order to kill them, etc.
You get points for how fast you get rid of the opponents and collect money to buy weapons and repair your Mech. There also are qualifying rounds between levels where you have to rack up a certain number of points by shooting enemies that scroll across the screen horizontally from both sides, similar to a shooting gallery.
DD is a strategy action game with lots of shooting, great graphics, tight gameplay and wacky characters, it has a high replay value ("just one more try") and is tons of fun. It's kinda cool to discover a gem like that on the Genny even after all these years.