Blue shift is, practically, any decrease in wavelength. Oh, wait, it is also the expansion pack (the 2nd one) for the critically acclaimed game Half Life! And this one was also developed by Gearbox. Interestingly, it came more than a year after Opposing Force, the 1st expansion pack, and while that one packed a punch, Blue Shift did not really offer anything new.
So, there is no real new content here: no new weapons, enemies or new music. But! It is Half Life! And also, you control Barney! The security officer who was bashing the door when you were riding the train with Gordon in the base game.
And this is why I liked in Opposing Force, as well. How the new protagonist's story was connected to that of Gordon. You could see a familiar locale in the distance (when in the helicopter in the beginning) or the aforementioned example of the security guard.
In any case, while Blue Shift did not really offer anything new (graphics-wise it came with a neat high-res texture pack, though), it offered the same cool atmosphere we loved Half Life for.
Blue Shift is a short but all the more entertaining ride! Highly recommended to all Half Life fans!