Um, are you sure you are looking at the right screenshots? The art is bland. The poly counts are extremely low. The shadowing and lighting are very simple. The geometry is primitive. And worst of all, it's not seamless. The textures on the walls don't perfectly blend into the textures on the ground. There's not bump mapping. This wouldn't matter if the textures were good, but they are not. They are plain, and low res.
And just so you know, Timesplitters 2 and Nightfire didn't have that great graphics...They were above average.
Prime on the other hand...is years beyond this game. Perhaps you need to play it again. Just look at the opening space station level...The transperancies, super detailed character models, advanced lighting and environment mapping, and perfect cohesion and seamlessness in the graphics, not to mention a great art style, all make Prime far better than Geist in terms of graphics.