To me this boss is too OP, especially if you using a caster… to many summons… to many cristal cast… to many life.
Hey, I dont want something easy, but guys, is insane. Summons, rats, fliers, dogs and moquitoes, and cast green meteors, heal cristal, green breath, green nova, obsidian spikes… come on.
I love GD, but every new boss is a new suffering…
He should generally be easier for casters than for melee, and I like fighting him as melee. Casters tend to have far superior AoE clearspeeds.
I don’t think he’s inherently any more dangerous than any other boss, he just demands you respect his abilities moreso than other bosses. Frankly that’s something more bosses ought to be like.
Agree with Ceno
Make sure you are leading him away from his crystal spawns. They definitely heal him and give him more speed. Possibly other things too?
I agree that the sentinel is a bit stronger against caster builds (depends on what kind of caster build it is tho)
most of my melee builds don’t have any real issues defeating him
still a lot of fun to beat him too death 
I think the summons are a bit much, but if those were slightly toned down, he would be in a good spot. I really like the fact that the crystals force the player to attend to the environment
Heal, speed, %OA and %DA. It affects his summons too, if they’re in range.
Never had a problem with my DW blademasters or 1H+S tanks.
I did run into problems with my vitality caster and my aether beam.
I think with melee characters, his attention is solely focused on what’s in front of him (aka you), no time for superfluous skills like summons and crystals 
He should still be summoning spawns and crystals even against melee characters.
This guy has ridiculous elemental resistance, no? I find physical and bleeding (and maybe piercing too) to do well against him, but it took ages for my Sabo and Elementalist to kill him on Ultimate.
Summoning actually hurts him by giving you good lifesteal or proc activation sources. If you are into that sort of thing, I guess. If he only spammed crystals and whacked you, he would be much tougher.
Shuffle your resistances around and you should be fine. Poison and lightning are things we ignored so far, so chances are those are not your strong suite.
nah I’m 88 poison and 83 lightning and he was still tough. My AoE dps was just too low to be able to handle his summons effectively and I eventually got overwhelmed by their sheer numbers. I ended up beating him after switching around my gear to give myself more armor and an AoE dps proc
It take me about 15min to down his life around the 40% with my Druid (Olexra+Trozan+Storm Totem)… I made a little mistake and boom! death, and his life uped to 70%… boom! another mistake and his life to 100%… and half and hour to go again to 50%…
That what I taking about… is boring. The same thing happened with Gonorrhea (Loghorrean) but was fixed.
He goes down super fast with poison
On my PRM Warlock I get swarmed every time. I feel like I have the DPS to kill him in a decent amount of time, but my lack of defense doesn’t allow me to keep up sustained dmg long enough to put him away. I need to re-evaluate my setup, skill point distribution, and devotions to be tougher while keeping the same amount of DPS.