I am pretty split when it comes to PvP, I played Diablo II for a long time which had no PvP system and no balancing done for PvP, it was just tossed in as a fun thing you could do. I also played Guild Wars for a while and had lots of fun playing Team battles and GvG battles.
GW was all about checks and balances, You fields a spike damage spell caster, we field a strong, fast casting anti-spell caster with lots of interupts to stop your spell caster, you field a fast moving, strong hitting build to stop our anti-caster, ect... The "Strongest" build changed from week to week as new ways of countering and one-upping each build was discovered. I really had fun with that but at the same time I thought that GW was missing a lot of the casual fun that was in Diablo II. I missed being able to challenge a friend to a 1v1 dual anywhere I wanted. For the longest time it was not even possible, and then when it WAS possible you had to go to a special location and if you wanted to change something you had to stop all the combat, go back to the common area, then start it back up.
So I really like the idea of arenas and not having to worry about some greifer killing me when I am trying to just play the game, I also miss the ability to easily change things up and just go on a casual killing spree against a friend. I mean towards the end of my playing time on Diablo II that is almost all we would do. We would play our new characters for a little bit, then get bored, grab a couple of our bigger ones and duke it out for a bit. It would ussually start because I would be out killing monstors, then my friend would join, we would have a really unbalanced level 12 vs. level 74 battle where he was restricted to only using daggers or something, then I would go get my high level and it was just fun. GW took that "just fun" out of the game and made it more standard. You couldnt just meet up with a friend randomly and start beeting the crap out of each other.
Man... I really need to stop writing these posts at 2:00 am...