Blue Shift is fun, but its over way too fast (contains spoilers)
If you've played Half Life or it's other expansion pack entitled Opposing Force then you know what to expect in this game: lots of puzzles and lots of action. You run around as Barney, looking through his eyes, as he clutches his weapons tights and fights his way through Black Mesa. You'll gather weapons like pistols, magnums, shotguns, assault rifles, grenades, rocket launchers, a crowbar, and others. All these will be used to fight off dog like things that send out shock-waves, Vortigaunts, tad pole like monsters that spit acid or whatever at you, and US Marines that were sent in to kill any living creature within Black Mesa.
The difficulty is a little hard, and the puzzles are a bit tricky. For example, to kill a US Marine (otherwise known as HECU Soldier) it takes like 5 shotgun blasts or 3 magnum shots, or the puzzle where you have to complete an electric circuit but the game does nothing to tell you how to solve it.... and you only find out by accidently moving a barrel in between the wires and the charge goes through the barrel.
The ending of the game was kind of lackluster, but certainly better then Opposing Force. You're helping Dr. Rosenburg and his colleauges finish charging this mini-teleporter. As you wait for the thing to charge so you may flip the switch and open the portal to leave, HECU soldiers come barging in. You fight them, open the portal and run through. You appear outside with the scientists who note that something is wrong - your glowing green. Quickly you teleport back to Xen (the alien homeworld). Then you appear back outside where you hear Rosenburg trying to figure out whats going on. Just as quickly, you appear in some sort of room and oyu see two HECU soldiers dragging an unconsious Gordon Freeman (the protagonist from Half Life) and saying things like "we should just kill him now." and so on. Then you teleport back outside and Dr. Rosenburg notes that your no longer growing green, that the scientists couldn't have done it without you, and all of you go driving off away from Black Mesa.
The only real downfall I have is the lack of action (fire fights) andhow short the game was. It was incredibly short.
Overall, Blue Shift was a pretty entertaining game when the fighting got hot, and to me it was a welcome addition to the series. Others may not like it but whatever. I give it an 7 out of 10.