The crazy variety of weapons and their interactions was great. Almost everything was dangerous in the right situation.
Blob gun? Charge it up! Blue laser thing? Shoot the ball form and shoot that for a huge boom! Double pistols? Max DPS in the game with no bullet curve!
The best maps too for CTF. Yeah, I loved that game, especially for in person LAN parties.
Requiring someone to provide evidence to back up a claim is not the same as taking a position that the claim isn't true. This is the root component of the burden of proof and the stance many people have towards a god claim: they aren't convinced the god exists due to a lack of evidence provided by the person claiming the god does exist. Until there's actual evidence it's rational and reasonable to withhold judgement.
The unicorn (or other mythological beings) are used as a similar case to illustrate to a theist that they have the same kind of attitude towards the idea of a unicorn existing as an atheist does to any gods. They're both neat concepts, but without evidence showing they actually exist, they're nothing more than an idea for stories and art.