I will begin my review by discussing the Slave Lords:
1) The quests had a nice length to them, but not too long. The mobs hit hard like bricks, as is normal for Legendary Elite, but not so hard that you're one-shotted, and the mobs compensated by not being giant bags of hp.
2) The presence, and placement, of traps in the first quest discourages zerging, which is nice, that and the mobs were in large enough numbers to kill you if you weren't careful. You made team work important again, which is great.
3) Fire Puzzle was a nice touch, and the presence of puzzles through out (I think) all of the quests were a nice change from the straight-up "beat-'em-up" formula that we had been getting.
4) A point unto itself, the DM narration by Willam from Critical Role was SPOT-ON. I loved the way he narrated the quests, and he may even rival the DM from old that did the narration for many quests (you guys know who I am talking about, the guy that narrated the OLD Gianthold, Shroud, and more), as he was my other favorite. It is my hope that he's here to stay for a while (don't get me wrong, his immediate predecessor wasn't too shabby either). My only comment on this front is I hope you guys can get Chris Perkins to do some of the DM'ing as well.
5) At first, I was going to complain that the massive grind for reagents was too much until I realized how powerful the loot is, and the fact that the ingredients themselves are unbound so they create a market.
6) About the only negative review of the Slave Lords that I have, really, is the loot. The loot is amazing, phenomenal even, and the devs did a great job with it. So what's my problem? The fact is, the loot is simply superior to EVERYTHING ELSE you can use at level 28 (with exception to a few items, and Legendary Greensteel since they can be used at level 26). My concern is that you're obsoleting your new content with every update, and while the craftable loot will take a considerable amount of time to craft and max (potentially, but maybe not if you have a whole guild pitching in and farming this stuff out), and this does more to harm prior content than help it (just like Restless Isles isn't ran for much of anything other than nostalgia, and other older quest packs are unpopular due to weak loot) - Epic Abbot is already obsolete on it's level 28 loot (27 is still "safe", but I digress).
The other thing is, the power level of this loot EXCEEDS even Raid loot, and it does leave me wondering how you are going to enable future content loot to compete without continuing the spiraling arms race of player power. I would like to suggest curbing the power a bit now and in the future.
Now as for Cannith Crafting (with some feedback/suggestions for improvement):
1 ) A major complaint shared by many (including myself) is the cost of raw materials required in order to craft much of anything - namely collectibles. The Purified eberron shards are not conventionally obtainable outside of favor tomes and epic token turn ins (and this for sub-level 20 loot). The costs do not vary, and while I can understand wanting a lot of materials for an epic-level power (especially ML 30-34), it is not justifiable when the ML of the item you're putting the effect on is beneath epics. This is something I've seen another Crafter on Lamannia complain about - there's more to the game than just the end-game, and not everyone wants to play the end-game.
With the way obtaining collectibles is currently implemented, it will take time to accrue many of these reagents because not all of the ones that you need can be obtained from dead mobs who occasionally drop a bag. The number of collectibles dropped (and found at stations and interactive objects) needs to be increased. I would also like to suggest offering these collectibles as end-quest, end-chain (in larger quantities), Wilderness quest objectives, and random loot chests. Another big issue is that you require many different varieties of collectibles, which may pressure a newer player into trying to research the wiki just to figure out where everything drops. For some (like myself), this isn't such an issue, but for those who baulk at the idea of needing to do research for a game (that they may only have limited game time for due to real life obligations), this would be a deal breaker.
What also needs to happen in my opinion is the weaker versions of effects should have a lesser cost associated with the lower ML of a given item while the higher level effects for a higher level item should be a little bit greater toward end-game. I am looking at the options for Kamgar (one of my alts that I brought along with me to test the power of cannith crafting since my main, Ziind, has many many levels into crafting) for his very first level of cannith crafting, and they're not terribly promising - prayer beads you can get a million of, and the wooden idols that are semi-rare you can get quite a few of. The problem, however, is that the OTHER ingredients are not quite so common, and you're wanting 15/5 for first level Cannith effects? The benefit for cost ratio is much too low for a new player stepping out of Korthos to justify asking for so many collectibles, especially since they can pick up random gen for no effort what-so-ever (which is what new players will do). Looking at this from the perspective of a new player, if the tutorials get updated, and I find I have sour luck with the random loot-gen draws (and tbh, in my first one or two years of playing DDO, I had AWFUL luck with getting ANY Named loot to show up in my name), cannith might be an attractive draw to work toward if I find I just can't ever seem to get anything more powerful to drop for me. Beyond that, it wouldn't be worth it until I've become much more wealthy (and powerful).
2) The Power level is passable for leveling, and equipping new alts you intend to create and play. When I brought kamgar along, he wasn't doing so great with his standard PDK starter loot. After cladding him in Cannith loot on all but two slots, I had Kamgar solo Missing on Elite, and he only died because the end-boss' prismatic ray procced an insta-death effect (which can bypass deathblock/ward anyways - TOEE taught me that the hard way with one of the optional bosses). However, the craftable spell-resistance effects stopped most of the mindflayers' mental attacks, the thaarak hound's phantasmal killer effects, and even the beholderling's many rays including ennervation. ML 15 for a total of 11 to any given stat is a nice touch, and the weapon damage was nice enough to enable the character to quickly dispatch mobs [I had two weapons, one with force, and the other light, and both had the slashing suffix]. [BUG BUG BUG] The only issue was that the stat damage effects were mislabled - instead of draining charisma and constitution as the shard claimed, it was draining strength and dexterity instead for some reason.
The system is not too bad if you're already an established player looking to "seed" a newly created alt. However, the problem is just that, you basically have to be an established player in order to craft some of the better effects, and with so many of the more powerful loot you keep bringing out every update being BTA, it would be so much easier for me to obtain those items and pass them down through the Shared bank, and my only incentive for fiddling with cannith would be to produce Stat items that cannot be reliably sourced anywhere else at that level range (one of the reasons I am cautioning against boosting the power of items every single update as you have been - because you are at risk of rendering an already shaky Cannith useless).
My overall thoughts on New Cannith is that it is in some ways weaker than the Cannith that is currently live (because you can currently craft an elemental of pure good with the current old system, but the new does not allow this, which I think is a bad idea). As effects go, Metalline should be restricted to the extra-slot so as to enable players to create their own boss beaters (ideal for new players who have not yet looted a named boss-beater, nor created one via Greensteel). It has potential to be useful situationally, but the costs have been laid out in such a way that you get more bang for your buck going for epic/end-game crafting rather than heroic crafting.