Watching the movie for the umpteenth time, I was struck by the illogic of Obi-Wan and Qui-Gon's reaction when first encountering Darth Maul. They seem clueless as to who/what he was. . .to paraphrase:
Obi Wan: "What was THAT???"
Qui Gon: "I don't know. . .but it was well trained in the Force!"
Maul looks terrifying, but this is the Star Wars universe. . .there are PLENTY of crazy looking species/races out there. It can't simply be his appearance. So: are we to understand that these two seasoned Jedi know nothing of the Sith???
At the time of this story, the Sith were allegedly "extinct" for well over 1000 years. They had survived and thrived, in secret, during that time, due to the whole "Master and Apprentice" thing. It wasn't until Palpatine, or as I like to call him "Ol' Palpy" came about, did the Sith finally have someone who was both powerful enough, and "mad genius" enough, to finally pull off a power coup, and overtake their ancient enemies.
So yes, for relatively young Jedi like Qui Gon (40s?) and Obi (20s) to encounter some being with Jedi-like training, it would, at that time, have come as a massive surprise. If Yoda had encountered Maul, being over 800 years old, he would have more readily been able to at least have an IDEA of what he was facing.
I don't buy that. Imagine if a rampaging army of horse archers, wearing fur-trimmed hats, started marauding about Asia. Would anybody go, "What is this!?" or would they go, "That's a Mongolian horde!"
There might be a bit of confusion, since they're so far removed from the present day that their existence is strange. The question might be, "Is that really a horde, or is this some weird cosplay/improv anywhere thing?" But even that only partly applies.
The reason Qui-Gon and Obi-Wan have no business not knowing what this is is because the Sith were the Jedi's greatest foes. I don't think they were meant to be extinct for millennia (correct me if I'm wrong), but even so, Qui-Gon at *least* would have studied what these are. This isn't like some cosplayer, either. It was Force adept and had a lightsabre. They don't know? Come on.