I have an affinity for slasher movies and horror movies featuring clowns, so with Terrifier being a heavy combination of those two things, it wasn't too much of a surprise that my overall enjoyment of the movie was positive.
Firstly, I'm going to mention the somewhat negative side to the movie with that being it's extreme lack of plot. To make things clear, I've never seen All Hallow's Eve yet, which is where this clown supposedly originates from and while I don't know if that movie contains some sort of backstory for Art the Clown, I feel that even if I had watched that movie, it probably wouldn't have made a difference to me. The lack of details left me feeling somewhat empty, like something was missing to complete my enjoyment of what I had just watched.
With that being said, the lack of plot and character backstory aids in the complete depravity of the character and of the movie itself. The movie is immensely gory and violent and since there's no real story to tell, Terrifier fills in the time which other normal slasher movies would be using to build character development and pushing the story forward with even more stalking and slashing. There's very little time to relax in your seat, there's no good time to take a few minutes out to go take a piss or anything like that otherwise you're going to miss something.
I had heard from others that the acting wasn't all that great but to be honest I thought it was up to par for a low budget slasher flick. David Howard Thornton does a fine job as Art the Clown, utilising a range of different facial expressions fitting for a character that goes from creep to freak in a flash. While no one else in the movie are all that memorable, they are all serviceable in their respective roles.
I haven't seen a lot of other movies that were similar to Terrifier, maybe the closest being Laid to Rest. They're both extremely violent slasher flicks and even though Laid to Rest does have a little more plot than Terrifier has, it's still really light on details and we also don't really learn much of anything about the character (at least until the sequel).