Bloody, addictive, fun as hell, and packed with adrenaline. Hands down one of the best FPS i've played.
I'll dive in straight to the single player first. UT99 story is simple: To win the tournament. You get to pick a team and name it. You basically go through various modes (Deathmatch, Capture the flag, etc..) until you fight the antagonist, Xan Kreigor, at the very end. You win trophies for your accomplishment of beating the various modes.
Moving onto the modes, they're are 4 main ones -- Deathmatch + Team DM, Capture the Flag, Assault, and Domination. I feel like i don't need to explain these modes except the last two. Assault, which consist of 6 maps, comes with simple objectives that you need to follow in order to succeed. There's the 'attacking' team and the 'defending' team that do just what it implies. This is an interesting and fun mode, but sadly not enough maps. The latter mode has you take control of specific areas that contain a symbol, which showcase the color of the team that's controlling it.
Other modes are arena style combat and a Chaos mutator which is included in the GOTY edition, and comes with a host of new weapons. Mutators basically change the gameplay to some extent. For example you can use a mutator that makes you jump a lot higher, or lowers gravity. It essentially bends the rules; if you want - it's optional.
Moving onto gameplay. Combat is fast paced and fills you with a rush of adrenaline. You can adjust things such as speed and AI difficulty to make this game as fast and hard as you want. The opposite is true as well. Let me say now that this was a very bloody game when it came out. And still is. That's what makes this game so much fun - massacring people up with various types of weapons. There are a whole bunch of fun, crazy weapons at your disposal. I won't go into detail but there's a good amount of them, each with it's Pros & Cons and each is useful for something. All the weapons are balanced, have two sets of modes, and are original. Onto the bots, they're very smart and challenging to this very day. This makes it so that you can easily enjoy playing UT in single player mode without ever wanting or needing to try multiplayer. And you'd have to be very good nowadays to play multiplayer against the remaining skilled players who still play. As for character customization, you get to pick different skins and race (Necris, Skaarj, even Nali - at least in GOTY edition) and voice, though i do wish you could custom your character a lot more then it gives you.
Graphics, even to this day (to me anyways), are fantastic! They were pretty 'stellar' when the game came out at the time. They were also improved over Unreal's, which were ahead of it's time when that game came out. Maps are greatly designed, too. Sounds are fantastic, not to mention the taunts that the players and bots say. The music is a huge highlight - it's what makes the gameplay and maps that more addicting. One of the most nostalgic soundtracks i ever have heard. You have your trance, electro, metal, etc.. all very composed well.
To top it all you can mod this game with all sorts of mods, which can greatly expand the value of this game.
Can't find many complaints to this game. Lack of single player isn't a fault, since this game is essentially the multiplayer part of Unreal. Customization as i said, could have been improved, as well as more Assault maps. But that's just me nitpicking. Any other issues is relatively small.
Bloody, addictive, fun as hell, and packed with adrenaline. Hands down one of the best FPS I've played.