These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
Contested Sequel: While the film was generally well-received, there's a significant portion of fans who feel it paled in comparison to its prequel.
Idiot Plot: Sure, go make out with your wife. Never mind the freaky eye or what she's been doing for the past months. Not to mention she probably knew that she was a carrier at that point or could kill an infected. Kudos to the military who leave her room unguarded, it's not like she carries a virus that killed dozens of millions the last time or anything.
And assuming Andy's the one who spread it there— and he probably is— he and Tammy are likely dead.
The Scrappy: The two kids in the movie. Not only were they largely responsible for the new outbreak of Rage Virus in Britain, but to make matters worse their selfishness causes the rest of the world to get infected, too. And yet through all of this, they still are the only ones who make it out alive. Ask pretty much any group of people who have seen the movie, and you'll find at least one person who was angry that the kids didn't die for their bad behavior.
Looking at the last shot in the movie, for all we know, they did.
The American military, consistently portrayed as unnecessarily authoritarian and violent, end up killing civilians by the truckload to contain the virus. Brutal? Of course. But if it had been completed, the continent (and possibly the rest of the world save for outlying islands and the American continents) would have been spared the rage infection. Instead, it's the compassionate turncoat who dooms humanity by giving the kids, WHO BROKE THE QUARANTINE FOR FUN and became unaffected carriers of the virus, a lift across the English Channel to safety. It's next to impossible not to root for the gun-wielding maniacs while this is going on.
Nobody knew Andy had become a carrier, since everyone who knew Alice had been one was dead (though the fact that Andy's eye looked like the eye of someone infected should have tipped the pilot off that something was wrong with him). And the military definitely held the Idiot Ball in a few places - herding all the civilians into one parking garage that obviously wasn't secure given how easily Infected!Don broke in is almost a case of Too Dumb to Live.
We saw at least one sniper Mercy Kill a fellow soldier that was getting swarmed by the infected.
Incinerating the infected area (and, Kill 'em All) is, in fact, the only sane method for dealing with a highly infectious quickly lethal disease spreading through a population. Once a virus (or other biological weapon-like disease) breaks out of quarantine into any substantial population, there's simply no other way to contain it. Physical geographic barriers (such as Britain being an island) can limit the possible spread, but, inside those limits, it's simply impossible to stop via normal selective targeting. All militaries use the methods described in the movie when dealing with that sort of situation, and it's not only the only effective strategy, it's also the only moral one - sacrifice some to protect many. Of course, given the Idiot Ball the US military had been holding up until then, it shouldn't have gotten to that point, but, once it did, ordering the soldiers to kill everyone (including uninfected) is the Right Thing.
Don's daughter berates him for not being sure his wife was dead. She completely ignores the fact that if he would have gone back to help his wife, the kids would have been out two parents instead of just one.
Don did technically lie when he said he'd seen Alice die. He can't really be blamed as he was too preoccupied with getting the hell away to confirm her death.
The Woobie: Alice cannot catch a break in this movie. Her husband abandons her when an Infected separates them, and he just books it instead of trying to save her. She is immune, however, and flees back to her house in London where she stays in hiding for months. She is eventually found by the military, who bring her back to District 1 and plan on killing her to run tests on her corpse to find a cure. Beforehand, however, Don visits her to beg for her forgiveness for fleeing, then kisses her... which causes him to become Infected and kill her in the most drawn out and painful death in the movie, all while she is strapped to a table. Then her body is lit on fire from the firebombing. Good lord.