It does come out of left field, and REALLY isn't what you're expecting. But I love that. The most memorable movie experiences come from being surprised, if you ask me. If you haven't been tipped off about the mysterious "thing" that makes these brothers so odd...you're in for a treat.
The cast is fantastic, but not stretching so much that it's palpable. The special effects come out of nowhere (seriously, it's like an oddly dark romantic comedy until they do -- then WOW) and they're great. The overall cinematography is easy on the eyes, the editing and sound are very good quality, and the twisted story unfolds without clichés. While none of these aspects individually make it a blockbuster, the "what the hell?" factor ALONE makes it a film treasure.
The people who bash this movie make no sense. It's one of those often-overlooked flicks of the 90's that you've either never heard of, or love so much you jump at the mention of its title.
I'm in the latter group.