Update: I was unfortunately not aware of Shamus Young's severe criticism of Fallout 3 available here to link in the original piece and I regret that. It dovetails rather nicely with what I've written and it's much better executed than my piece. I strongly recommend anyone...
Descent 3 is played in a truly three-dimensional realm. The simple explanation is that the player flies a craft that is completely immune to the force of gravity. That doesn't mean gravity doesn't come into play from time to time, but the craft is truly zero-g. That's where the simplicity stops. As with previous excursions, players must maneuver their fighter through tight areas and be able to fight effectively against intelligent enemies who are often as aware of their surroundings as the player is. The difference between d3 and d2 in this regard is that the indoor areas look like facilities and power stations and cities, while earlier games simply had boxes connected in appealing ways. D3 also ventures outside for the first time in the series. The seamless movement between indoor and outdoor areas was something to be said for a game of its time. Descent 3 also features three player ships, intelligent robots, new weapons, and somewhat of a storyline (though that's obviously not the main focus)
Image yourself as a fly. You've seen how a fly gets around right? Up, down, back, forewords, the fly can go in any direction with a simple flick of the wings. Now put that fly in a zero-g environment. Assuming the fly can comprehend what to do, directions suddenly become meaningless. The fly can be uspide-down as easily as rightside-up. Such is the case with descent 3. Any possible directions can be acheived at any time with the correct implementation of control. Due to this complex system, the player either needs to have a joystick with a hat switch or extreme dexterity and a keyboard which accepts alot of commands at once to even be able to fly, let alone fight. However, once mastered, the player can experience a sense of freedom unparalleled by practically every other game they could play.
Depends on your point of view. If it's 1999, your computer will struggle to play it. If it's 2005, your computer will laugh at it. It's simplest to say that the graphics were awesome for it's time and leave it at that.
This game has it all. Out of the box, it comes with a metric ton of fully-funcional multiplayer modes, including anarchy(deathmatch), team anarchy, capture the flag, hoard(collect the green balls), robo-anarchy(anarchy with robots), co-op, and entropy(kill enemies to gain viruses, then use viruses to take over enemy bases). The community has enriched this supply, with dozens of modes including assault (your robot army vs theirs), instareap (instagib), guardian (kill their guardian to steal their flag), and pyromania (classic ships with not-so-classic graphics). Descent 3 used to have a dedicated multiplayer service, but that was shut down some time ago. Instead, the community has pulled together and created standalone servers with a dowloadable tracker. In the end, it's actually quite a bit more efficient than the original service, allowing for chatting and detailed server information before the player gets into a game.
As opposed to earlier versions, descent 3 has an objective-based system. In previous games, it was just get keys, kill reactor, leave. In d3, you might need to rescue a downed fighter or protect reactors so your comrades can escape. The story plays into the single player experience more and each mission starts out with a detailed briefing of what you might encounter.
Descent 3 is one-of-a-kind. A fine wine and an endangered species all mixed into one. There's never really been anything like it and we're not likely to see another of this ilk for a long time. With such a unique experience and a community that is still going strong with new levels and active servers, this is one that's hard for a discerning gamer to pass up.