As much as so many of the elements of this film work, it's main problem is that the story Beyond the Gates presents comes across as hollow.
There's a plethora of things to like about this film. The whole 80's aesthetic, from fantastic synth music to creative lighting, was fantastic. A few good gore scenes within also, and most of the characters themselves (especially the two bothers) are pretty decent.
Acting was a mixed bag. The brothers (Graham Skipper and Chase Williamson) worked well together, though Skipper's acting, at times, was a bit dicey. Williamson was pretty solid throughout. Barbara Crampton (Re-Animator, From Beyond, and Chopping Mall being her classics) was nice to see, despite most of the time she just stared awkwardly into the camera.
Matt Mercer (probably best known for his role in the Contracted films) didn't have much screen-time, but was decent when he appeared. While I didn't care for Justin Welborn's character (and he didn't really seem to add much), his resume's pretty impressive: aside from this, he was in 2007's The Signal, 2008's Dance of the Dead, The Final Destination, Halloween II, My Super Psycho Sweet 16 (despite the title, that movie was actually pretty good), Southbound, and some film's I've not seen, such as The Crazies remake, The Bay, V/H/S Viral, and Siren. Basically, if you've seen much modern horror, this guy might stick out. Lastly, there's Jesse Merlin, who plays a goofy store owner. He had a pretty fun presence.
Still, despite a moderately strong cast, the story still came across as rather shallow. Great gore at points, along with well-done 80's nostalgic aesthetics can only do so much when the story itself is lacking. Especially in the last 15 minutes of the film, things begin to fall apart, and the previous ominous feel the film had sort of gets thrown out the window. I did like the idea that the brothers were fighting to save their father's soul (given how different the two brothers are, it was a fun dynamic), but there's not enough meat.
Beyond the Gates certainly had potential. What they do well, they do really well. Again, I'll direct your attention to the film's score, filled with fantastic music. The special effects, lighting, and gore were all expertly done. But in the end, the film's just missing something, and because of that, despite all that this movie does well, it falls below average.