Broken Base: The canonicity of Portable Ops is heavily debated. Some fans still consider the game to be canon because it expands upon some of the details that was referenced in the ending timeline of Metal Gear Solid 3 and the core story foreshadows the events of Metal Gear Solid 4. Others consider Portable Ops to be non-canon because Hideo Kojima didn't direct the game. Officially, the game is canon, but Kojima has said other games can and will take liberties with it.
Contested Sequel: Portable Ops bears the distinction for being the only mainline Metal Gear Solid game not directed by Kojima himself and has a peculiar position in the series' canon as a result. Initially advertised as the "missing link" between the events of Metal Gear Solid 3 and the original Metal Gear, it essentially tied up all the loose ends between those two games (showing how Big Boss first formed FOXHOUND, met Roy Campbell and Frank Jaeger, and obtained the funds for Outer Heaven) and even foreshadowed the events of Metal Gear Solid 4. However, despite the generally positive reception it received during its release, Kojima was unsatisfied with Portable Ops and went on to direct the next PlayStation Portable game in the series, Peace Walker, which he wrote as a direct continuation of Metal Gear Solid 3, ignoring everything that happened in Portable Ops aside from a single reference in which Kazuhira Miller tells Snake that they can finally "leave all the crap in San Hieronymo behind."
Deader Than Disco: You can tell Konami doesn't care about this game when they had several compilations of the series and only once did they include Portable Ops.
Game Breaker: The M870 shotgun is ridiculously effective against half of the bosses (namely Python, Null and Gene).
Jerkass Woobie: Cunningham is pretty much a big jerk and somewhat two-faced towards FOX and the CIA, but considering what he had to put up with (being forced into a desk job after his leg was amputated, not to mention learning that the CIA basically left The Boss to die, which in his views was an insult to the memory of the Mother of Special Forces), it's kinda hard to blame him for what he did.
Recycled Script: Grab Metal Gear Solid. Replace Solid Snake with Naked Snake, Liquid Snake with Gene, FOXHOUND with FOX, Deepthroat with Ghost, and some other changes and you'll get the script of Portable Ops.
Scrappy Mechanic: Whose bright idea was it to have your teammates die permanently in combat? Fortunately, this was remedied to be more tolerable in the sequel.
So Okay, It's Average: At worst, the game is regarded as enjoyable or at least accepted as part of the series, except it delivered far less than was promised.
Villain Sue: Gene. Compelling Voice/Charm Person, beats up a one of the strongest Metal Gear characters in battle and has them as one of their minions, is an evil counterpart to Big Boss like Liquid is to Solid Snake, is a Super Soldier/ultimate battlefield commander, has Super Speed, and created his own upgraded version of CQC. Not even Ocelot or Steven Armstrong were this bad.