Just chiming in with my experience, though obviously it's quite a subjective thing.
I've only played since the 0.3x days, but have always done so with Dwarf Therapist, and never really liked DFHack's autolabor. I preferred the granular control of Therapist & creating custom professions, etc. and would enjoy figuring out where to sort each member of a migrant wave to use their talents best. However with the excitement for the Steam release I just couldn't wait and have been giving it a go anyways and I gotta say... at least personally, I think I actually prefer this system overall to using Therapist.
To be clear, I have complaints about the new labor system and Steam release in general: removal of "only dwarves above X skill level" option, not always listing all relevant skills / traits when selecting a dwarf (e.g. squads only show weapon skill, not amor/dodging/etc. Capt. of the Guard doesn't list social skills, etc.) a lot of menus I wish were searchable, or menus with dwarves listed where I wish I could click on a dwarf to see their stats page, really wishing there was a "cycle to next dwarf" button when viewing a dwarf's skills so I didn't have to jump in & out of the main unit list to hunt for a certain skill combination, burrows not able to designate more than 1 z-level at a time, no persistent event log, and more than I could list here.
However I consider all of that par for the course in terms of following a game like DF, hopefully some of those issues will get addressed after feedback, some might require modding to replace down the line, worst case some features will just be sorely missed, but the big thing for me is that even when Therapist comes out for the Steam version, I'm not sure I'm going to want to go back to it. It took a few days to wrap my head around the new labor system, but eventually after combining the default work details, setting workshop masters with a few extra workshops, using the specialization option on both certain work details and certain dwarves, and a few custom work details, I feel I generally have as much control as I used to. Or at least as much control as I wanted to? I haven't even made use of burrow restrictions in combination with all of this, which could add another layer on top, e.g. an "Mass production" burrow that only low-skill level dwarves are allowed in, to make sure any work orders on those workshops are things I don't care about quality for.
Using the workshop master + specialization on the dwarf in particular has been big for me, doing that is almost like setting a "mini-profession" without having to make a new work detail, since I know that dwarf will only work on the 1 or two things I have them set on, and I can control which work orders go to the shop they are master by setting its limits on general work orders. For skills that only use a single type of workshop, and that workshop is only used for a single skill, this has been great, E.G. a few kitchens & stills each with a master set who is "specialized", thus no need to make a cooking or brewing work detail. Or a metalsmith forge with a legendary weaponsmith set as the "specialized" master, set not to accept any general work orders.
Overall the way I'd describe things, at least how it comes across to me, is that the old DF + Therapist was sort of "High specialization, that you need to opt-out of if you don't want it". I.E. everything is very granularly controlled, and if you don't want each dwarf assigned to do very specific tasks, you would need to put in some effort to set things up differently, e.g. enabling a labor on all dwarves.
The new system I'd call something like "A very generalized, streamlined system, but you have the option to opt-in to high specialization for some or all aspects as you like". I.E. by default it just sort of makes sure everything gets done, whether or not its efficient or effective, which is probably great for new players but not what many veterans want. However when using enough of the new features you can get a ton of control back, in the aspects you want to.
I wonder if part of the issue is that veterans may see how the new system is set by default (super-streamlined) and assume that's the only way it can be used, without any options for fine control without making dozens of custom details like how you would use Therapist? Again, this is just my experience and not meant to take away from the many valid criticisms there are. I'm quite fortunate that most of the criticisms I have so far are things that don't happen to overly bother me much (or I've been able to tweak a bit with some modding).