Deus Ex is arguably one of-if not the best game of all time. Why the bold statement? Besides pioneering many new techniques in gameplay, and seamlessly integrating RPG elements into it, Deus Ex features rich and complex subject matters, touching the nature of human society and government.
This is my favorite game of all time. The game is one of the first to allow multiple ways to pursue objectives (stealth or guns blazing), and you can customize your character to suit these playstyles. The story is rich and engaging, full of cyberpunk and conspiracy elements. You might find the game more relevant today than players did back in 2000, which the overtones of corporate power and surveillance. 10/10.
The original Deus Ex executable was made during a time where CPU governors were primitive at best. Nowadays dynamic clockspeeds mean that the game won't be able to anticipate changes in speed, resulting in nasty speedups/slowdowns. To solve this, Deus Exe was created. You can replace the Deus Ex executable in Steam as well!
Admittedly, Deus Ex has some flaws, most of which are due to its age. There are multiple mods which seek to improve/overhaul the game, and others which make an entirely new game.