I read a novel years ago called The Somnambulist whose narrator was extreeeeemly unreliable. The protagonist was a Sherlock Holmes type and the prose was really sarcastic about him, always digging into his faults. I thought the author had it in for the archetype and was just trying to dismantle it, but....
spoilers
It turned out the story was being narrated by his Moriarty all along, and the final act shifted to their first person present tense point of view.
Which was really interesting, though not well handled, because the plot by then was dissolving into chaos and nonsense. Everything in that book was "really cool idea, bad execution." But I still remember the twist fondly, because suddenly it made sense why the protagonist was so pathetic, hahaha.
That's the unreliable narrator I like - ones where you can trust that the events are actually happening, but the perspective on them is slightly different. When a narrator is SO unreliable that you're not sure WHAT happened, or have to ask ~is this character even real~ I lose interest. Ambiguity in a story is great but there are times when the creator pushes so far that it shatters their trust with the audience, and it starts to feel like cheating (aka Heavy Rain, even though I personally didn't have a problem with that one because I liked the character so much).
So I guess as far as advice goes, I would say, above all else, don't LIE to your reader. Everything else is fair game. And remember that you chose your protagonist and their specific point of view for a reason. Things outside their POV, even if objectively true, might not matter to the story as much as you think it might, so don't feel the need to reexamine their POV unless that too is part of the story.