The biggest minus comes from the source port selection. Authors have selected to use DooM Legacy, which has more bugs than all other source ports together! Some to mention, the game can crash when you load a game or exit a level... Sometimes it also crashes without any visible reason...
Anyway, you can also play this with ZDooM! With ZDooM you miss one little pool of water, but you get working sounds and no crashings at all. That's a good trade I would say :)

Graphics
I might well be that some of the graphics are stolen from other games/add-ons, but I'm not sure. Anyway, that doesn't matter at all! All the new graphics look cool and fit perfectly to the theme.

Sounds
Sounds vary from good to excellent. Too bad that if you play with DooM Legacy (a.k.a. Duke DooM) you won't hear them all, coz the current version of Legacy is so damn buggy! Here's another reason to use ZDooM instead of Legacy :)

Monsters
Instead of beasts and monsters you are fighting against humans and dogs, and that my friend gives a big boost to this game! Nothing is more enjoyable than killing one of your own kind in a game :)
There are several different human types in the game... All have different weapons, but I think they are at least almost as easy to kill...
One exceptional enemy - or should I say enemy vehicle - has gotten it's way to this game. That vehicle is known with a name helicopter! Yes, that's right, there's a helicopter in the game!!! Check the screenshot!!!

Hostages!!!
I believe that before Twilight Warrior, there was add-on called Hostage Resque... Anyway, Twilight Warrior has hostages, and you must protect them, not kill them. Killing them ends the level (duhh) and you can consider your mission to be failed. Of course you could cheat the level through by just killing the first hostage that you see, but as I said that would be cheating!

Weapons
Weapons of this baby rock! You get the long distance rifle (really cool) and machine gun right in the beginning. Long distance rifle is my favorite, though there isn't much use for it. Later you also get hand grenades and also a rocket launcher! Only lame weapon in this pack is the knife. It looks and feels really lame, but I had no use for it at all. Then there is one more weapon that totally rocks too! And that is the flame thrower! Specially on SVGA mode it looks fantastic (see the screenshot).

Levels
Mostly these levels are really good and fit well to theme. Some of them might be a bit more detailed, but theres not real need for more detail. There are different kind of levels! Jungle, city, enemy base, ship! Overally really great! And few of them are made by one of my favorite level designer Kurt Kesler! :)

Final comments:
Twilight Warrior is exceptional add-on with great feel, graphics and enemies. The biggest flaw in it is the engine that it's made for (DooMLegacy). Good thing is that you don't have to you it to play this! Avoid the bugs and flaws of DooMLegacy by using ZDooM!

Here are the stars that tell you how good is it:
The look: Very good!
The sound: Mostly very good.
The feel: Very good!
Hardness: Mostly hard enough.
Mindwork: Minimal.

Points:

Twilight Warrior homepage: http://www.doomworld.com/twilight/main.htm

Go there and download it!