I dont really like the Devotion system either. Those are just passive stat increases such as +10 phys/c/spirit or sometimes resistances (those I like but I bet they will get useless with legendary gear in the game) or maybe health/mana regen. Or you get some proc skills that you have to associate with a skill to even allow them to level up. There are no skills on the tree that you can just take, even stuff such as turtle shell that activates when you get to low life requires to be associated with an aura/buff to work.
Another thing I dont like about it is that shit is difficult to clearly see. The zoom out level is not enough to see the whole thing at once, and the constelations are too close to each other, and not bright enough to clearly see where is what. I do have a real trouble with finding constelations on the tree.
I dont like the "unlock" system for constelations. You need to gather enough of those "aspect points" and how do you get them? By completing constelations. The problem is, that you get them only when you complet a constelation, taking all the stars inside it. If you just wanted to take the three first stars because you needed the resistances and wanted to skip the last two stars because they give spirit or some useless shit like that, you will not get any aspect points and wont be able to progress further into the tree. So you either take some inefficient/useless for you stars or you get no way to progress to the more usefull constelations, and some of them require a lot of the aspect points, like 20+ which with the limit of 50 devotion points would require almost exclusive focus on completing only the constelations that give a fair amount of this particular aspect points. For example, there is the constelation that requires 20 blue aspect points, and to get that many blue points you would have to complete around 6 other constelations of maybe 5-6 stars each. If you even would have access to so many constelations that give a lot of blue points without investing into some other constelations to get red/gold/whatever aspect points to unlock the blue giving constelations. And all that while getting shit that is of no use/or very little use for you build like mana regen for my Warden (I never get under 80% mana), or spirit or piercing damage increase or stuff for pets or shitload of stuff for shields only etc. And in the end, when you finally get the aspect points to unlock the constelation you want, it is nothing gamechanging, it just gives you more stat increases, just bigger ones.
Yet another thing is, that I can hardly find anything on the tree that would be really good for my two handed melee build. There is nothing exclusive for it (There is something for two handed ranged even, and shitload for shield builds). All I can take as a two handed melee a one handed melee can take too, and he can use the shield focused constelations too.
All in all, I use the devotion system to just get more resistances or life (around 11k life right now on my Warder).
But can we take a moment and discuss the resistances? Who the hell thought that it will be a good idea to have 10 resistances in the game? Good luck trying to get decent resistances to all of them. Every fucking enemy group seems to have their own "element" with shit like aether/chaos/vitality/bleeding/piercing damage that is something completly separate from fire/cold/lightning/acidpoison damage. And then you have stun resistance and a stat that decreases the freeze time, because aparently the cold resistance is not good for it. And the worst thing about it? There is no indication which enemy mob does what type of damage. Sure, there are the basic, common sense rules that when somebody throws fire at you, you use fire resistance, but what about all the demons and Cthonics? Do they use chaos? Bleeding? Vitality damage? Who does use aether damage? Only aetherials? Or mages too? It pisses me because I have no idea which resistance I should increase not to be hit so hard by Chthtonic Bloodletters and Harbringers. Those are the only enemies that will destroy 5k of my hp very quickly. But they do similar damage to my other chars with less hp, so I suspect that their damage may not be flat but rather %based, which is fucking stupid.