Just did my part, and gave them my feedback. The following is a copy 'n paste of it. Feel free to add your own. I'd love to read it.
Killing Fields - Respawn Timers and Difficulty
Respawn timers are set too low. Enemies often seem to respawn almost instantly after getting killed. Killing an enemy feels like it has zero impact on the gameworld. A circumstance that can make the experience frustrating. Especially when exploring Tyria on my own.
TTK (time to kill) seems a tad bit too high overall, which further amplifies the problem of too short respawn timers. Shaving off a couple seconds of average TTK on every encounter, and significantly increasing default respawn timers, could do wonders for Guild Wars 2, as far as I’m concerned.
Killing enemies has to become more rewarding – and I’m not talking XP and gold and loot. I’m talking of killing enemies and let them be dead for awhile. Let their broken and defeated corpses bare witness to my power and progress. I vanquished these foes! I am the victor – and this is my killing field.
Of course I’m not against dynamically decreasing respawn timers to accommodate for large groups of players, but killing foes should feel more impactful than it does now. Semi-instant respawns do effectively deny such satisfaction – and can become gamebreakingly frustrating.
Cheers, and many thanks for the awesome that is Guild Wars 2 – respawn timers not withstanding.