Seeing as how pretty much all groups are out of the raid by now and it probably will not open up again this beta weekend, I will talk about it now and shed some light on the boss and my opinion.
Vale Guardian is the first boss of Spirit Vale. The boss is split into 3 phases and 2 add phases. The first phase goes from 100% of his health until he reaches 66% of his health. At this point, he will split into the 3 trash mobs that were faced previously. Once those 3 mobs are killed, he will reform and phase 2 begins. Phase 2 is the same as phase 1 except that he adds more attacks. Once he reaches 33%, he will split again, then you have to clear the 3 trash mobs. Once trash is dead, he will reform again (Phase 3), and will proceed to continue out the fight with some more new mechanics.
I will not describe the mechanics of each phase too much in detail since this post will be extremely long, but I will say the fight itself is not over complicated once you understand the general gist of it, but it is a long one, and 1 mistake from any member of your raid and you will be in trouble of wiping.
My main concern with the fight is the timer added to the fight. You have 8 minutes to complete the entire fight (all phases) otherwise the boss will enrage and gain a 500% damage increase in which he will proceed to 1-2 shot most players. The fight feels very over-tuned and I believe will require some number adjusting from the devs before launch. Without talking specific numbers, the boss itself has a lot of health, so much health that you would need to have the raid pulling a very high dps in order to down the boss in the 8 minutes given. It is difficult to achieve this required dps even standing still and not worrying about mechanics unless you min/maxed the entire group. Talking to a few groups that got to attempt Vale Guardian, none of them were able to successfully maintain that level of dps, while doing the mechanics of the fight on top of it. Also, the fight has two add phases as well, with the red guardian being a purely condition only mob, meaning you have to account for this as well when min/maxing. Brainstorming with other players, it appeared that an optimal composition would have 1 player tank the boss, 6 players in zerker gear, and 3 players in sinister (condi) gear in order to even have a chance at killing him within the 8 minutes. To claim that “the berserk meta will die” with raids coming out is a very false statement when looking at this boss in its current state.
Overall, I believe the mechanics and the fight itself are fair and doable when not under the pressure of a timer. The boss has enough mechanics to where groups will wipe often enough to them alone. I believe that the timer at least needs a 2-5 minute increase in order for the boss to actually be killed within the timer if Anet chooses to go the timer route.