I finished Area51 today. The last 1/3 rd of the game was the best. Still lots of endless waves of enemies spawning one after the other, but still better than the initial levels. And the CGI work is just awesome. Great movies indeed.
It seems to me like the level designer of the last levels was not the same from the first, since the last were far better in quality than anything from the first few levels. The effects were better, the animations were better, everything was just so superior. It´s like there were 2 seperate games. The first was crap, while the second was a masterpiece. I guess the quality product manager slipped up...
But i couldn´t find one single bug throughout the game, wich is rare indeed.