Well I spent the weekend mostly playing a Mesmer, I can see this being my main come release, was a lot of fun to play. I did try a Ranger but found the pet would just pretty much always die quickly and I would spend half my time patching it up, whether that improves with levels I don't know but it was pretty annoying. I tried both a Warrior and Guardian and can only say lolmelee to that.
As the Mesmer whilst bimbling around in WvW I had quite a few 1v1s which I lost a grand total of 0. The high damage, high control and high mobility just seemed too much. I was playing with a Staff / Scepter-Pistol, I essentially would only swap to the staff for the field that damages/fears them and spent most of the time with the scepter/pistol which had very high damage output (same dmg auto attack as the staff but attacks seem much quicker) as well as a long range multi-target stun (the ultimate anti-runner ability

). I had also maxed out my damage going for full power on all gear including trinkets / rings etc, then maxed out domination for even more damage, glass cannon worked whilst everyone was low level, whether it works at 80 would be interesting to see. Plus there was one amazing trait speciality that at 25% hp would replace me with an illusion and put me into stealth, can see that causing a lot of wtf's
It did lack that heavy dmg AoE during keep sieges that my friend playing an Ele was getting to go mental with, also your illusions / phantasms don't attack doors and can't get to the people inside so a large portion of being a Mesmer seems to be suspended during key parts of a siege. Perhaps siege cannon monkeys would be better suited to Mesmers in sieges both attacking and defending.
I found the difference in levels to be huge in WvW -- at lvl5 my staff's auto attack was doing about 150~ dmg, at lvl20 that was 450. So people wanting to level WvW when there are actual lvl80s about are going to be a massive detriment to a server as they will just be complete fodder if that damage keeps scaling like that.
I quite liked the dynamic events etc but it wasn't as 'explorable' as I felt it was made out to be, basically there is a breadcrumb trail you follow as theres only a couple of things in your level range at any given time. When watching the Yogscast videos of them just 'going wherever' they were lvl30+ running around a lvl15 zone. I also did feel that lack of XP in Kessex Hills, I ended up about 4-5 levels behind the next lowest quest available to me at one point -- now whether or not this is down to tuning or the game or they intend you to go to the other races lowbie zones I don't know.
But can't wait for the next beta weekend -- going to try the Ele / Necro properly next time, hope theres much more optimization to performance as some of those WvW fights we're pretty laggy to the point where I preferred being in small groups defending supply camps and the like.