HALF-LIFE: OPPOSING FORCE / Valve / PC
Opposing Force is an official, commercial add-on for Half-Life published by Valve, but they actually outsourced it to Gearbox Studios rather than putting the same team responsible for the original game on it. It's still faithful to the tone and style of the original though, largely because it changes next to nothing, just gives you a bunch of remixed maps to play in the Black Mesa/Xen setting of the original game.
There's a new single-player campaign with a new story that is significantly shorter than Half-Life - it runs about 4-7 hours as opposed to the 12-15 or so it took to grind all the way through Gordon Freeman's tale of alien woe. This time out we're Adrian Sheppard, a fresh new Marine captain assigned to an advanced special forces squadron, and guess where we're going to wind up headed to. The big twist in this one is that you're playing as the forces that invaded Black Mesa and were slaughtering scientists, trying to NEUTRALIZE. FREEMAN. and etc. The game gives them an out early though, as your squad never even gets its orders as the squad commander is rudely interrupted by an alien missile to the face before he can repeat them, and then its just chaos from there pretty much. You start out being helped back to consciousness by a scientist and you'll have cordial if somewhat tense relations with them throughout the game, no wholesale slaughtering. Instead you're following a path somewhat similar to Freeman, just trying to survive and escape after seemingly being abandoned.
But first up, there's an optional training level that highlights what little new gameplay bits there are to the game. This follows Sheppard during his boot camp days, in which tired old Full Metal Jacket cliches are wheeled out one after the other in a halfhearted attempt at humor. The engine is fundamentally unchanged, the weapons and items mostly just have little tweaks to them. Adrian now has night vision goggles instead of Freeman's janky flashlight, there's a new knife weapon for melee combat, you get a pipe wrench instead of Freeman's duelist crowbar, and there's a selection of new heavier guns, some of which have been borrowed from Team Fortress. The worst new addition, however, is the ability to swing on ropes. Rather, I should say, the *necessity* to swing from rope to rope at certain points of the game. If you thought the climbing/jumping mechanics were already janky and frustrating, you ain't seen nothing yet. Seriously, the "rope swing" physics in this game were so bad they nearly made me quit it all by themselves, just because they bring everything to a screeching, horribly frustrating halt whenever they show up. But I pressed on (with a bit of cheating here and there) to do my due diligence in reporting.
My first play of the story mode immediately introduced another major problem with Opposing Force - lots of glitches. At least the first one was entertaining - during the non-interactive opening cutscene, Adrian somehow managed to immediately run out of oxygen and die, yet the whole sequence kept rolling on, so I got to take it all in from Corpse Cam. On the second try, it worked and I was able to actually play the game. The game repeatedly liked to freeze, however; it's especially finicky in elevators for some reason, a long-running bug that I've seen posts about on forums that are years old yet seemingly never was fixed, at least in the most recent version obtained from Steam.
I had heard that Opposing Force enjoyed two big advantages over Half-Life - a dearth of annoying jumping sequences, and the ability to command up to 8 troops with improved AI and squad tactics. Both of these turned out to be terrible lies. The bulk of the first hour of the game consists of annoying finicky jumps over instant-death sludge pits, and that's before you even get to any of those rope-swinging sequences I harped on about earlier. And the Marines? Not only are situations rare where you have more than two or so available to follow you at a time, they seem to still have the same shit "following" AI routines that the Barneys and Scientists had in the original game.
The game's saving grace is supposedly awesome multiplayer maps composed by an all-star team of nerds such as Levelord, but since barely anyone plays this anymore, it's now become kind of irrelevant.
So, given nearly useless multiplayer, tons of glitches and freezes, frequently frustrating solo campaign level design, and a general stale taste due to lack of new content, I have to say you're really not missing anything if you skip this one.
* Gameplay Video