Hey all, I've just tackled the Artificer, so roughly halfway through the alch playthrough. Here are my observations so far.
First let me say that I love the lack of summon timers. I've always felt like a proper summoner should spend more time supporting the minions with other skills rather than managing cooldowns constantly, so it's already better than vanilla in that regard. Unfortunately there is one major issue it shares with vanilla, and I'm not sure if this can be modded or not, but minions are largely ignored by enemies. They can't really tank for you, and end up running in circles chasing the enemy as the enemy runs in circles chasing you, which is all rather silly. If at all possible, please address this.
Onto actual skills, lets start with Nether Imp. They're reasonably effective in combat, and the raising from corpses effect is pretty cool, however there's one big problem. There are many situations where they are impossible to use at all. You may be surprised how many types of enemies leave no corpse to begin with, not to mention how often corpses explode when you hit them hard enough. Also, the game seems to deliberately explode corpses in major boss battles and phase beast challenges wherein waves of mobs are spawned, to prevent them from piling up. From past experience, this will also affect endgame content like Tarroch's Tomb. Add to this the fact that minions disappear on map changes, as well as the game removing existing corpses if you reenter an area, and you see that the Imps are underutilized. My recommendation is to allow summoning a minimum of one imp per cast, even with no corpses present, and amend the description to say you can lure more out of the nether realm by offering fresh corpses (also explaining why the static corpses encountered in the world don't work). And as a minor side note, the nether imp footstep sound effects wear on my nerves after a while. I'd really prefer them to be muffled if not silenced altogether.
Next summon, the Alchemical Golem. I think this has a lot of potential, especially if the general problem with enemy AI can be addressed. However, the golem desperately needs a move speed buff, as it spends the majority of the time trying to catch up to the rest of the group, often arriving just as the battle ends. It could also use some knockback resistance if it's going to tank properly.
Thorned Minions is a nice idea, but the aforementioned issue with enemies ignoring minions makes it wholly irrelevant.
On the more active side of things, Ember Bolt could use a little fine tuning. The damage at Tier 0 is strictly inferior to auto-attacking with the first wand you pick up. It becomes serviceable once you're firing at least three bolts, but it should really gain an additional chance to poison, with poison chance and poison duration increasing by rank. Compare to its closest kin, Prismatic Bolt, which I suspect it was cloned from anyway.
Ember Lightning damage also feels a little low, and the sound effect volume is much too loud.
I love the concept of Ember Barrage. It's like a magical minigun, and actually quite potent once it "spins up". I'm not so much a fan of the aim-assist on it though. Much of the time it arcs around what I'm trying to shoot, completely missing even stationary targets at short to medium range.
Ember Lance is much easier to aim, but the damage is almost nonexistent. It really struggles to break shields or penetrate enemy armor even on normal difficulty.
There are some irregularities in the alchemist skill tree in general: Nether Crystals and Ember Sentry requiring level 28, and Alchemical Powder Bombs and Ember Phase requiring level 35. These all deviate from the standard progression of Tier 1 to Tier 7 skills. There's also the fact that several alchemist skills do not improve with ranks except via tier bonuses. This has an interesting impact on character progression, which may encourage players to try out a greater variety of skills since Rank 1 is just as good as Rank 4 with less mana cost. It's also somewhat convenient for my purposes of playtesting the class for the time being, but assuming this was unintentional, it should maybe be addressed at some point.
I'll be back with more input, most likely after I track down my doppelganger.