History YMMV / HalfLifeOpposingForce

** The squad mechanics in general are quite underutilized. Particularly when it comes to the HECU Medics and Engineers. There are only 2 Medics you ever come across in the game to take advantage of their healing ability. Meanwhile, there are only 3 Engineers in the game, and their ability to knock down doors is quite rare as there are only three doors throughout the entire game that require an Engineer to knock down. In addition, only one of the doors is optional as the other two are plot-forwarding {{Locked Door}}s, and the last Engineer you meet up with in "Foxtrot Uniform" doesn't even come across any doors to open (he's instead used to open the grate to access the surface where he and his squad are hiding; this is a railroaded scripted event).

** [[spoiler:The G-Man puts Shepard in indefinite detainment. One of the most common questions you'll ever hear about a potential new game in the ''Half-Life'' universe is if Shepard will finally make a comeback]].

** The idea of playing as Marines trying to stop the Xen invasion and hunt down Gordon Freeman is awesome, but that gets thrown in the bin as soon as the game starts. Shepard arrives during the height of the Marines' losing battle at Black Mesa, but gets knocked unconscious and by the he awakens the war is over and Shepard is forced to work with the Black Mesa personnel to survive. Functionally, there's little difference between Freeman and Shepard, which is a pity.
** The idea of Shepard being a HECU marine who never got the orders to dispose of Black Mesa's employees, which in turn makes him come off as friendly to the surviving employees, is also an interesting idea that's never truly delved into. Not once is Shepard's loyalty ever put to the test where you would think that he would stumble across some worker-killing HECU soldiers, which they would find it odd as to why Shepard's not taking part in axing off the Black Mesa employees with them. The result is missing out on what could have been a bit of inner turmoil going on amongst the HECU.

** The [=MP5=] really gets the shaft in this game. The amount of souped-up enemies introduced in ''Opposing Force'' renders the [=MP5=] a mere pea-shooter compared to the player's other options. Even still, the game encourages its use way more than usual. Ammo is ''way'' too plentiful; the weapon is already ubiquitous among Black Ops agents, but 9mm pickups are among the most common in the game. They also yield double the usual amount of bullets than in the original ''Half-Life''. Thus, it's common to have a lot of unused 9mm ammunition sitting around where other ammunition could've been placed.

** The Barnacle Grapple, due to the fact it turns one of the series staples into a surprisingly useful tool, and for making an otherwise creepy enemy [[UglyCute kind of adorable]].
** Shephard, for being a military AntiVillain analogue to Gordon Freeman. Him earning the attention of the G-Man and the ambiguous circumstances of his fate has left fans begging for Shephard to make a return in a spin-off game.

** The [=M40A1=] Sniper Rifle may look like just another run of the mill rifle, but when you actually fire it, each bullet deals 100 damage - greater than that of a direct hit with a ''rocket'', with more common ammo to boot (though it was still uncommon compared to the more contemporary firearms). Combined with the fact that (prior to a later update) it was 100% accurate even without looking through the scope, it made many multiplayer games very, very easy.

** The [[WrenchWhack Pipe Wrench]] suffers noticeably from the game's poor melee combat mechanics due to its slow swing speed, meaning it is quickly outclassed with the introduction of the Combat Knife, which pairs the Pipe Wrench's higher base damage (10 damage) with the Crowbar's faster swing speed (240 hits per minute). Despite this, the Pipe Wrench still stands out thanks to its more powerful alt-fire attack, which (depending on how long it is charged) can deal anywhere between with the 45 and ''200'' damage - enough to instantly break large crates and down a Shock Trooper on ''Hard'' difficulty in a single, well-timed swing! It's this, alongside the many similarities it shares with Gordon's Crowbar (first weapon found in the game, everyday mundane tool-turned melee weapon) has cemented its status as Shephard's signature weapon.

** The [=M40=] sniper rifle has its two firing animations [[note]]One for cycling the bolt normally, and one for just opening the bolt if the shot that was fired was the last shot in the magazine. The latter is because the empty reload animation involves closing the bolt to chamber a round after changing the magazine, while the non-empty reload is just a quick magazine swap.[[/note]] swapped with one another.
** In certain briefly-seen parts of Xen, the skybox appears to show faded, semi-translucent electron microscope images against a mostly purple backdrop. While this is perhaps cool to look at in its own, it isn't sold well as an AlienSky (especially when compared with ''Half-Life'') and looks rather lazily done.
* ThatOneLevel: "Crush Depth" and "Vicarious Reality" are probably the first really difficult chapters in the game. After being teleported to Xen briefly and then returning to Earth, Shephard finds himself in an underwater laboratory long fallen to the Race X enemies, with the occasional classic Xen alien here and there. The Race X aliens are far deadlier than their Xen counterparts, and with the Black Ops taking an absence in these chapters, supplies are scarce. It is also home to a number of platforming puzzles and labyrinthine levels that can overwhelm a newcomer.

** The idea of playing as Marines trying to stop the Xen invasion and hunt down Gordon Freeman is awesome, but that gets thrown in the bin as soon as the game starts. In fact, Shepard arrives during the height of the Marines' losing battle at Black Mesa, but gets knocked unconscious and by the he awakens the war is over and Shepard is forced to work with the Black Mesa personnel to survive. Functionally, there's little difference between Freeman and Shepard, which is a pity.
** The idea of Shepard being a HECU marine who never got the orders to dispose of Black Mesa's employees, which in turn makes him come off friendly to the surviving employees, is also an interesting idea that's never truly delved into. Not once is Shepard's loyalty ever put to the test where you would think that he would stumble across some worker-killing HECU soldiers, which they would find it odd as to why Shepard's not taking part in axing off the Black Mesa employees with them. The result is missing out on what could have been a bit of inner turmoil going on amongst the HECU.

** The Spore Launcher is a repulsive alien creature that Shephard can use as a weapon. But if you hold still for a bit, [[http://youtu.be/J06tqrJt6pE?t=7s Shephard will pet it]] and for a moment it’s just adorable. Its reload animation is also quite cute since you literally feed it ammunition which it happily chomps down.

** ''Opposing Force'' offered a few gameplay mechanics not seen in any of the other games such as using a detached barnacle as a grappling-hook and rope climbing.

** Shephard is never given the order to silence Black Mesa personnel, so he's just another average Joe trying to survive the hardships of Black Mesa alongside the scientists and security guards, plus his own HECU comrades, instead of being the bad guy and having the former two be hostile. The HECU and Black Mesa [=NPCs=] are neatly segregated throughout the entire game, with the only possible mix up being the end of "Missing in Action" where one of the first soldiers Shephard can command can spot the hiding scientist in the shaft, and go hostile.
** The squad mechanics in general are quite underutilized. Particularly when it comes to the HECU Medics and Engineers. There's only 2 Medics you ever come across in the game to take advantage of their healing ability. Meanwhile, there's only 3 Engineers in the game, and their ability to knock down doors is actually quite rare to see as there's only three doors throughout the entire game that requires an Engineer to knock down. In addition, only one of the doors is optional as the other two are plot-forwarding {{Locked Door}}s, and the last Engineer you meet up with in "Foxtrot Uniform" doesn't even come across any doors to open (he's instead used to open the grate to access the surface where he and his squad are hiding; this is a railroaded scripted event).

** Race X is actually hostile to the Xen aliens, but you won't know that unless you do a bit of file mining, or if you take too long in killing the Gargantua on the dam, as the Shock Troopers that warp in on the other side will attack it once they've killed the HECU soldiers in their place. Otherwise the two alien races are never seen in the same area.