One of the best PC games ever. Super combination of RPG and FPS elements. Really engaging characters, situations and dialog. JC Denton, one of the coolest agents ever. Great main theme music. Many different routes through the game for great replayability, with three significantly different endings, way before multiple game endings were at all common. And all the other things already mentioned. Still have the disc, have it installed actually, and it runs fine under Vista with nVidia graphics.
Invisible War? Meh. Seriously dumbed down compared to the original. And also doesn't run under Vista.
As far as weapons from the game, I'd love to have a GEP Gun! But more realistically, that 10 mm Stealth Pistol was pretty cool, it would be great to have a red-lit LAM or two, and I'd love to have a whole bag full of EMP grenades. Fry bots, fry!