Likes: I like how MW fills feature gaps, i.e. add stuff that's obviously missing and should be included in vanilla but hasn't been done due to the development scope. This includes features like the disease system, poison coating, the pantheon system, druidism, machinery, archaeology, etc.
I also like how it keeps up with dfhack development so I don't have to manually fetch every single plugin one by one if I want to test the latest features, which used to be a thing not so long ago.
Dislikes:
The animal revamp: it's just too confusing to have leatherwing bats and dew beetles and suchlike. First, they're not canon so it's "stuff someone thought would be cool", as someone in this thread said. Sure it's cool but it breaks the immersion and doesn't preserve the DF look-and-feel, which I believe was one of the avowed objectives of MDF. Second, you have to manually look up each and every animal to see what it does and completely change your management. Plus they're counter-intuitive. When you have turkeys, cats and dogs, you expect them to behave like turkeys, cats and dogs. Who the hell knows by heart how strong are boulder craps, how fast they breed, how much time they take to grow, etc.? At some point you stop treating leatherwing bats as actual bats and just see them as "flying leather generator", which is too gamey for my tastes.
Any non-canon mention of Armok in the game. Armok according to canon is the entity that generates, runs and reforges worlds, it's beyond worship and it certainly isn't equivalent to the procedurally generated gods. In my opinion "shrines to Armok" and such are cheap and don't respect the DF lore.
All workshops should be symmetrical. It doesn't make sense that you can only build some workshops from East to West or North to South. Also they should be 3x3 unless they represent extensive industries like siege engines, this would greatly simplify and reduce management pain and doesn't force the player to carefully dig every specific room for every specific workshop. Plus some of their requirements are absurdly difficult in comparison to most vanilla workshops which just require a block or a boulder. Most of these "specific workshops" don't have a mood associated to them either.
There are too many races. Since most of them are hostile it's just "generic enemy level 1", "generic enemy level 2", etc. with gimmicks, increasing difficulty and loot rewards. Since most of them are not canon they don't have an associated lore to them beyond generic stereotypes; they don't have associated sites or language files (as far as I know) and overall not as much thought put into them as for the canon races, which again breaks the immersion and doesn't preserve the DF look-and-feel; in other words I feel like I'm playing some weird LoTR spin-off instead of Slaves to Armok: Chapter II: Dwarf Fortress. Gnomes' features could very well be ported to Dwarves' without much loss, and Orcs are simply custom goblins. Succubi are just completely silly, even more silly than concubines in my opinion. I think you could cut the whole civilized races to Dwarves, Elves, Humans, Goblins, Kobolds without altering much of the actual content. Seriously, do we really need a whole civilization for Automatons or Frost Giants? Having them as megabeasts is fine; whole civilizations of them is just weird.
There are too many metals. Bloodsteel, bifrost, volcanic steel, etc. Again, they're not canon, and they're not realistic on top of that. I don't exactly know what I'm looking at when dealing with new materials. Microline I have a clear idea. Bismuth bronze? Sure thing, I can look it up. Now what the hell is bloodsteel? Steel with blood in it? Blood forged into steel? How do you set its melting point? What's its Young modulus? Why should it behave differently than volcanic steel? Realism is an important part of the game. Sure the vanilla game has adamantine, divine materials and whatnot, but they're hidden, are full of dangers and Toady has a long-term vision for them. Are you sure that you aren't going to scrap volcanic steel after a while?
Changelings and Djinns are way too silly to be casually embarked with. I know it's fun to randomly generate objects or creatures but it's yet another case of breaking the immersion. A smarter choice would be to have Djiins come up as rare animals or summons or something, and you could catch them and tame them.
Streamlining materials is too gamey to my tastes. Part of the whole game's charm is to be able to craft bolts from the forgotten beast's bones you've just slain.
The carp god doesn't belong to the game. Keep the community stories and bay12 references to the community and bay12.
In retrospect I realize I have been exceedingly harsh and I didn't expect my post to turn into a huge rant. Of course, you should know that we always notice what doesn't please us first, and this doesn't affect in the least the good features that have been added and mentioned above.