PK for me is that you use a tactic, then it stops working, then you have to use another one, then it stops working as well. Your opponent
is a player who can read your moves, if you can read what happens but do nothing about it - woe is you. The best PK experience I've had in CF were when my standard tactics didn't work. Once I've been fighting Zugnu as Grokko for like five hours straight? Dude's been burning through my spiders, killed me thrice (exactly when I tried standard tactics), I've been burning through his skins, looking for a single chance to make each other die, because we've been fighting each other so much we knew almost all possible options, and that's where the true fun of PK starts.
And in the example above, that was bash-monkey vs trip-monkey 5 hour match, resulting in no bash and no trip used (well in fact Zugnu was tripping me, which was hilarious).
On the FPS-comparison. I don't play FPS and consider them shit games. My favorite games are CRPG and the process of building your death machine is part of PK experience for me (I
love spamming skills btw).
CF gives me experience of designing (like that character is something I've created through my cunning and time investment) and then utilizing what I've built in a competition against others. RP lays out the environment.