First off, points go to the director for sticking with a simple bit of motivation for the opening title: when in doubt, use the same font as numerous 70s horror classics. Anyways, he also does well at manipulating a wind of dread among viewers that blows in with the genre standard of doors opened to unrelenting monstrosities. Why call it a wind? Because it's continually shifting in regards to the mannerisms of the so-called guest, David Collins.
WHEN that door opens, of course there's no escape. But Adam Wingard wasn't looking to make a gross-out competition entry. He's aiming for a thriller where everyone is off their guard, especially the audience. And how does that work? Through constant mood shifts that eventually leave our initial expectations null enough to wonder what's gonna happen. Is he or isn't he? Will he or won't he? The mood shakeups are constant enough to coax a unanimous gasp more than three times. It was also a wise choice to make the explanation behind such motives subtle and limited, so that it's not hammered into our heads. Not even the secondary outside party is blatant enough to pause from the budding tension and inquire what's going on, despite their doofus organization name (Uh hurr hurr hurr, K.P.G. because PUTIN!).
If it was anyone other than Dan Stevens, however, the degree of difficulty in throwing off viewers would elevate. Here's an actor that came out of nowhere (nope, never watched that show either) to pull off a military vet stranger covering his mental scars with a "make things right winningly" approach. Every exchange of dialogue involving Collins is an awarded score for his side.
The movie's tension works through the well-aged plot device of one character (in this case breakout actress Maika Monroe's Anna) discovering some peculiar things about the mystery visitor while everyone else deems him a saint. The weak point in all this, however, is the tendency of Anna (whom might I add Monroe paces well in her suspicions and frustrations), her friends, and family (featuring Leland Orser as the supporting cast highlight) to acquaint with and react to David in a fashion that can best be summed up by the following: DUMB!
I agree, having a large concentration of idiot characters extends the anticipation of what will happen and provokes greater audience emotion that helps to make the viewing experience fun. In "The Guest," though, the supporting characters' word choices and decisions feel like a social ineptness contagion instead of a few minute yet fatal flaws. Even the introductory talks contain a dash of dumb. The family members could have been intellectually respected more through, hmmm, having more than ONE dialogue exchange about David that wasn't within David's hearing range. Amongst other things that are soaked in spoiler. Whether this was intended homage to the genre trademark of victim stupidity comes down to director confirmation. Okay, one spoiler: nor did it help to have Anna's confrontational moment end up as a "Cry Wolf" declaration instead of something more "Game, set, match." I don't know, something at the level of flashing the ring while descending the stairs in... that Hitchcock movie for which you'll have to sit through his filmography to find.
Despite that, "The Guest" sets up the classic trust manipulated plot point through the humorous demeanor and caring nature of a brotherly figure likely either good, evil, or both. It's a performance by Dan Stevens that is able to captivate the viewer with a level of charisma as welcoming as his actions are horrifying, something perhaps seldom seen since Dr. Lecter himself.