So far I have only played a Rogue, Nightblade or Assassin to be more exact, and I find the diminishing returns unbelievable to be honest.
I play Assassin, I have an opener which stuns for 4 sec, does some damage (quite a burst, but definately not more than 10% of a targets health on a crit), gives 2 combo points (3 talented) and costs 50 energy. This is an obvious opener, as it ends up dealing more damage than Assassinate on armor heavy targets, and the 4 sec stun is good against both melee classes and casters (the damage is water based).
That is all good, but it only stuns for 3 sec instead of 4 on an enemy. That would be fair if you had something to follow it up with. Oh, I actually do!
I have this ability, costs 20 energy, stuns for 4 sec, no damage, and has a 30 sec cooldown. Nice one, another 3 sec stun on a player. Ehm... No, in fact it stuns for 1 sec if used after a stun-opener. This makes this spell worth nothing but a 20 energy interrupt on a 30 sec cooldown in PvP. Since rogues have close to no survivability (we do have some, but no heals or other crazy cc to get a breathing space), controlling our enemies is essential.
To sum it all up, I think the diminishing returns in PvP are way to punishing. What are your thoughts on this matter?
Another subject I would like to get others opinion on is the use of arenas. Now I used to be a wow fanboy until the release of Cataclysm, and PvP have always been a major part of my gaming experience in mmorpgs. Diminishing returns aside, I think Rift would have the potential of taking PvP to a higher level by introducing arenas, as I find Warfronts extremely gank'ish with people runnning around in a group, focusing one target down at a time. Ofcourse there are exceptions, but I'm sure you've experienced this matter aswell.
tl;dr: what are your thoughts on diminishing returns and eventually implementing an arena system that has some of the same qualities as World of Warcraft?