I was surprised when OP gave CoC a thumbs up. Leprechaun is at least creative.
I think OP and I have similar thinking...Leprechaun is a fucking killer leprechaun, just by renting it you are agreeing to suspend disbelief and have fun. Michael Myers comes off as being believable, possible, credible, but then fails to follow though on that promise.

I hated the 28 Days/Weeks franchise for that. We start in a lab, all scientific, then we get grumpy zombies with no attempt at a coherent ruleset for how they behave. Zombies were originally a voodoo thing, yet all the zombie movies make it scientific, but then the zombies fail to be scientific in any way, just magical.