Opposing Force is a game that changes and rise what an expansion pack is mean to be.
Even being older as the original game, Gearbox show us, again, how to do things. First, in Half-Life, they show to us how to make a masterpiece. Now, they show how to make a true expansion pack for its masterpiece. Technically, there is nothing that wasn't polished compared to the original.
Presenting a new character, we take the role of a soldier from the US Marines, with the mission to capture Gordon Freeman. Named Shepard, we must infiltrate Black Mesa complex, survive and fight through the big mess and find the scientist that started all – Freeman.
"Survive?" You may ask, "But if Shepard is together with the army, why he must survive?" many can ask like that. But this big mission pack has this objective, show to the player which was the situation of the army, while it was trying to execute the "clean up mission". Not only that, but new alien species will appear. Big and scare ones with different abilities that didn't appeared in the original game. Ah! Have to mention that a new type of some kind of "black ops" is also present here, to increase the mess.
For all that, Gearbox just raised the difficult to another level that we were not close to see in Half-Life. The original game had a great difficult progression, but was never that difficult, being nicely tuned in all moments. But here in Opposing Force, this is not what happens. With all those new enemies, expect a lot of tighter situations.
But Gearbox, again, would not raise the difficult like this if it wasn't a way to counter all that enemies and hard moments. I think there is at least the double of weapons in this expansion compared to the original. Three new melee weapons and two new groups of weapons, including two new amazing alien weapons, sniper rifle, a powerful machine gun and one experimental weapon/device – more on it later. Believe me that all those new weapons are great to use, feel powerful, useful and fun to use.
In the original game, we had a straight line in the evolution of the game, what is called a very linear game, where we must follow, what seems sometimes, a huge level. This expansion going to that way too, but, instead of only way to explore the game, usually, we have some extra paths and "hidden" rooms that will almost always contain precious ammo, health and armor, or even anticipating some new weapon, like secrets, and is easy find them through all the game.
Also, there's an amazing new weapon in the game, an experimental weapon that fires something like a vortex, with the same appearance of a portal, that kill any enemy with a single shoot. But, the best isn't that powerful shot, but its secondary fire mode, that works like a personal teleport, where, in some moments, we can activate it and go to the alien word, always to places where we can gather some more supplies.
Also, for the fact that Shepard is an army man, every time that we encounter or rendezvous with other military or squad, we can ask for their help. Well, not that is a help, but Shepard will always be hierarchically superior than the others soldiers, making them always follow our orders. There three types, one being a key to solve some puzzles and other useful and the others supporters for the fire power. The engineer will open sealed doors and medics will heal our wounds. Unfortunately, I found their path finding abilities very limited and dumb.
My last point will be about the sound effects. Most of them are recycled from the original game, but the new elements were greatly made and sound amazing. There's also some few music, but nothing that hold our attention. Even the environments effects having a great and more important role in the original game, it's still great here.
In the appearance, is almost identical to the original game, with some improvements, like better textures and great animations. But it could had make all the difference if would made in the new Quake 3 engine, instead of the Quake 2 engine. But I'm not complaining… is just an observation.
So, Opposing Force is a game that changes and rise what an expansion pack is mean to be, with a great pack of additions more a new side, complementing the original game. All this is what made this game so amazing and solid. I just recommend to anyone that played Half-Life or not.