Just in case any of us design a PvP ruleset for a massively multiplayer online game, Scott Jennings has helpfully posted a 13-step guide to "PvP done right" on his personal blog, BrokenToys.org.
It's a potent mixture of common sense, personal opinion, and thousands upon thousands disagreeing that classes are needed. It's a great primer, aphorisms or not, and written wonderfully. Put simply, PvP in a game needs to work -- if it's an impossible concept or impossible to implement, nothing else matters. Personally, I'd go as far as to say the simpler the concept, the better the execution -- of course, that's a huge sweeping statement, but be it Team Fortress 2 or World of Warcraft or Chess, the depth doesn't come from the rules, it comes from the implementation. Except Cricket.
All decisions will upset someone. It's just about having a realistic, well-defined goal for PvP in your game and going from there -- and accepting that there will always be an awful lot of criticism, rage, and Fury.