I'm going to make a few assumptions here. The first being the folks who typically really dig the pot-smoking, drug-induced haze in their films likely don't read reviews about it. The second is that the people who do read reviews still go to the theatres, and at least in some cases (my mom aside), they're looking to prove the reviews wrong.
Picking up just hours after where we left off in "Harold & Kumar Go to White Castle" (never mind the 4-year-gap), Harold and Kumar are heading to Amsterdam, in pursuit of Maria, the girl of Harold's affections. They get through the airport (with only a small amount of name-calling between Kumar and a TSA employee) and onto the plane, where Kumar reveals he's smuggled weed and a smokeless bong onto the plane.
After some turbulence, the bathroom door flies open and a passenger sees him and yells about seeing a terrorist as he lights up his bong. Kumar tries to explain it's just a bong, which sounds like bomb of course, and the two are tackled and arrested as terrorists. An over-zealous Homeland Security guy Fox sees them as part of a sleeper terrorist cell, and they're quickly shipped from New Jersey to Guantanamo Bay.
The film is brought to us by the dynamic duo of Jon Hurwitz and Hayden Schlossberg, who wrote, produced, directed and acted in "Harold & Kumar" (both films). And that is also the end of anything they are credited as having written, produced, directed or acted in; 'nuff said.
The film appeals to a particular niche of the population, so folks like mom who are reading reviews won't give this one a second look. They are huge in the under 18 and 18-25 group, however, and the audience reaction reflects it. You have all the earmarks of a rebellious youth culture, which is something the H&K films have brought to the screen: rude humor, rampant support and use of marijuana, and toss in a bit of random blood splatter. Y'know, but just a little.
John Cho (Harold) and Kal Penn (Kumar) do quite well given the materials they've got to work with in both films. Penn has managed to step out of the sophomoric humor in some recent roles that also show his maturity as an actor and his range far exceeding how long he can inhale smoke. ("The Namesake" come to mind.)
All told, it's neither a bad film, or one that is going to be fighting off four others in an Oscar list. And if you're a brazen, non-review-reading teen, you'll thoroughly enjoy it. For the rest of us, it may not be your cup of tea... and if you're mom, trust me on this one and instead take in the film in the next theatre instead -- you'll thank me.