Personally, I dislike PvP, but understand it can be useful, even needed for a dynamic RP world. Doesn't mean I enter into it, I'll try and avoid it in most games if I can. Unless that's the focus of the game(League of Legends).
My problem with PvP is often the risk involved.... I don't like risk, go figure >P. But there's also the fact that PvPers -tend- to be the most toxic players in the game by nature, because all they care about is how big their "e-peen" is, and how they can kill everyone in the game. All they care about is the PK and how it makes them feel great, and not how it makes the other people--who may not want to be involved in the first place--feel.
Serene is a nice way to combat it, but it isn't -always- RP viable. I would avoid PK and go serene outright if I could, but Daklore's roleplay doesn't -allow- for the OOC serene mechanic to be applied. I've accepted that, and in the past, I used to be involved in PK. But, if you remember, Fuzzbutt, Daklore only pk'd as a last resort, or a response to an action that called for violent retribution(mostly the Tyrek-Mventious war, the Klevnone-Tolin wars when I was still in Tolin ... and those people after my bounty).
The problem with KotL is, PK is inherently unbalanced. There's only one or two ways to go about it, both require you to be customed out the wazoo, and in most cases, once you've got augments, there's only one way to go about it. I won't reveal the way, so people will abuse the hell out of it, but it's rather anti-fun when you -have- to min-max to even hope to be successful at PK. Yes, min-maxing exists in other PvP games, yes some people find it fun... but games existing around the PK mechanic can exist without the min-maxing, and min-maxing can often only return minimal benefits. Well, extreme min-maxing. There's always going to require some sort of focus around the kind of class/profession/whatever you're playing to optimize your strengths. But it doesn't require extreme maths to squeeze every last point of offense and defence you can manage to get out of it.
KotL requires this, though. It shouldn't. Skills are underpowered(with some noticable, but minor, exceptions), spells are overpowered, resistances are overpowered, anyone who isn't a fighter or mage is pretty much frakked... and there's simply no reason to PK when you know the hard-coded mechanics have already determined the winner before you fight. Unless you have the same min-maxed build, then it comes down to who gets lucky first.
tl;dr: PvP can be nice and beneficial, but only if it's well-balanced and constantly tweaked to make sure it remains balanced. KotL does not offer a balanced approach to PvP, therefor, it's unfun.