If you are willing to put in the effort Fire Warrior is a mediocre FPS at best.
While the story itself is presented quite well, the voice acting is not quite the best. The Tau all sound a bit off, little passion going into it. The Ethereal and the Tau Fire Warrior captain are really the only good highlights in the Tau voice acting, but even they arent that excellent.
Some missions require you to do absolutely hair splitting objectives. Near the end of the mission, you are required to take down a Chaos dreadnought, but this can get extremely stressful, as the Machine is more then capable of taking you down in one or two hits.
The only way i was able to defeat it in the end, and most of the more difficult enemies later, is by abusing a bug, where you would run Kais straight up the them and fire, and the AI would be incapable of aiming at you. As mentioned above, some enemies are extraordinarily difficult to take down until later in the game. For example, a chaos obliterator who appears near the end of a mission, killed me in two hits flat before i knew what the hell was going on. Another downfall is the save game function. You cannot save mid mission if your in a difficult situation, you must start from the last check point triggered, which can get rather irritating especially when approaching near the end of a mission.
Overall, Fire warrior is OK. Not excellent, but not trash either. If your willing to spend a few Dollars or Euro for this in the bargain bin, it could be entertaining but dont expect anything spectacular.