Took down the Vale Guardian last night in a pug (actually got into a full group by typing 'LFR Exp Chronomancer). I had 80 or 90 mag shards from previous pug attempts before taking it down. It was an extremely satisfying kill, and I feel like my DPS and utility has been well tested. I cannot stress enough how, as a Mesmer main, Chronomancer has been the best part of the expansion for me. What a glorious fucking elite spec. Alracrity makes everyone happy, and I feel powerful and useful in just about every situation I've been in.
I have at least one of every class up to 80, but I barely play any of them in PvE except for Mesmer. None of the other classes click for me, or if they do, they feel too familiar (Reaper, though, may be an exception from what I've tried so far in PvP). In fact, since launch, I've effectively only played two weapons on Mesmer: Greatsword and Staff. I strongly believe that I would've gotten bored with the game years ago if it weren't for GS Mesmer and shatter builds; it just feels so good and unlike anything I can get in any other game.
Up until Vale Guardian, every single dungeon and fractal (well, never really got into fractals), I've played with GS/Staff. With VG, it became clear that I had to bend my style to cater to this fight, and it didn't feel comfortable at first at all. Instead of Staff, I took 1H Sword+Shield (1H Sword on Mesmer is practically essential for one of the phases where constant boon strip is necessary). As the attempts went on, Sw/Sh finally clicked for me and became extremely enjoyable - I've never before enjoyed 1H Sword on Mesmer.
By the time my group downed the boss after 15-20 attempts last night, a part of me felt a bit naive for sticking with Staff in single-target PvE content for as long as I have been. Now I'll never give up Greatsword in almost all situations, as the range and flexibility for my shatter style is too good, but 1H Sword and Shield might be my new permanent secondary for even open world PvE now, and I know I wouldn't have been pushed to try it without Raids and the harsh DPS timers that come with them.
In fact, getting to the second Spirit Vale boss (which appears to have an even tougher DPS timer, though the only attempts I've had against it are learning attempts), now I'm starting to feel the inflexibility of stat shifting. I know Legendary Armor's selling point will be stat changing any time you wish, but I think stat flexibility will be just as important for raids as it is for PvP. I believe it's time for Anet to consider allowing players to more dynamically switch stats with Ascended Armor (maybe by first 'feeding' the armor Orichalcum Insignias or something, but being able to switch freely between the fed stats after that). Zerk Mesmer got me past the first boss, but I feel that I'll need something different for each fight if the second SV boss is any indication of what's to come. I like adapting, I just don't feel like the tools are there yet to make it ideal.