It does its job. It would also tie the engine to Windows, losing the portability advantages that rival OGL based engines have. In one area though, the engine did impress. The outside areas are used to good effect with vehicles available on a few levels. Terrain features are fairly low-poly for the most part, allowing for satisfying sniping across impressive distances, without the jarring blockiness found in Unreal for example.
Progression is fairly linear.
Whilst slightly disappointing this is for the most part to be expected. A slight annoyance is that several missions are required to end in 'failure' because the plot demands it. A nice feature is that you can choose to access any mission after you have progressed to it in the course of normal play. As you've probably gathered, overall I rather like this and think it is one of the best FPSs of 2000 and certainly the most fun. And if you don't, buy it anyway.