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. Not helping matters is how the game has been seen by Konami and Kojima since the release of Peace Walker.note It is barely acknowledged in official Konami press and media, it wasn't included the compilations Metal Gear Solid: HD Collection and Metal Gear Solid: The Legacy Collection, and Kojima considers it to be a spinoff.
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 positive reception it received during its release, Kojima 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.
Game-Breaker: The M870 shotgun is ridiculously effective against half of the bosses (namely Python, Null and Gene).
Jerkass Woobie: While Cunningham is pretty much a big jerk and somewhat two-faced towards FOX and the CIA, 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.
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.
Vindicated by History: With certain contestedtitles in the franchise, depending on who you ask, it's now considered as probably the best of the non-Kojima Metal Gear games, as it's the one that held truest to the series' core concept.