I've been greatly enjoying the mod (basic, not challenge) over the base game so I thought I'd give some feedback.
When I embarked I think I counted 9 new hostile civlizations, not including goblins, elves, and humans. I think the hellfire imps were missing. The world was created over 600 years, and only one dwarf civ was available at embark (one that hadn't figured out high boots as it turned out).
I'm in the summer of my third year, 66 dwarves. I haven't used danger rooms or traps, beyond one line of outside cage traps meant to catch wildlife (i.e. elephants) relatively far away from my fortress, and a set of cagetraps in at the entrance which haven't been used yet. My main military force is 3 axedwarves, all in steel, who have ended up repelling all invasions up to now. I also have 4 marksdwarves who still use wooden bolts and are mostly there for the experience, and 7 hammerdwarves strictly training for now.
Until this summer there was no real threat - I'd get goblin ambushes, frogmen, dark stranglers, furies (who are completely unarmed and unarmored - I think this is a bug).
This summer however I got one squad of blendecs - took a bit longer to slaughter but still no threat, and a squad of nagas - the bowmen were a threat, the swordsmen were not although again significantly tougher then previous enemies (I ended up having to restart the game a couple of times so I got to see both bow and sword nagas). And also 2 (or maybe 3) goblin ambushes - not a problem except for a lasher that injured one of my axedwarves. Along with probably 2x squads of fury "bowmen" (again no armor/weapons), 3x squads of frogmen and another 3x dark stranglers who pretty much all ran when I got into contact with one of their squads and slaughtered them. All these enemies came together probably within a month of each other, and they were all driven off/killed.
Along with them however, I got the real problem which was a squad of nightwing swordsmen (about 10 probably) using steel/iron weapons and armor. I think the main problem here is actually that my axedwarves can't put on their gloves properly so any long fight eventually ends with them being hand-less. Which wasn't a problem before since the enemies get slaughtered quickly but the nightwings do not die easily, at all. My marksdwarves with copper bolts also can't seem to do much damage to them. They hit, they "chip the bone" but they don't bring them down, even if they are all firing on just one enemy.
The good thing is that the nightwings are apparently not interested in attacking me. They sit a fair distance away from my fortress, and wait. I've tried a couple things - drawing them out in small groups with the marksdwarves - doesn't work too well since the marksdwarves have really bad defensive skills, so I need to intercept them with my 2 healthy axedwarves, who usually draw out 6-7 nightwings, and kill 2-3 of them before loosing their hands. I also tried to use my 7 unarmored but well armed and decently skilled hammerdwarves, to charge in after the axedwarves but they got slaughtered. I think I'll try to somehow get around the gauntlet bug and give it another shot at some point.
So some questions/issues I've had:
1) No elves came, ever. And I'm pretty sure they were there on embark. The humans came the second year, but it's now autumn of third and they didn't show up this summer. I don't know why - we traded fine before and there have been no casualties for traders.
2) I've had no ambushes from all the new races, only sieges. The goblins are the only ones who ambush. Don't know if that's intended
3) As mentioned furies are unarmed/unarmored
4) Dark stranglers are butcherable. Is this intended?
5) This is probably something that you cannot change easily (or at all), but probably my biggest gripe with the combat system in this game is how much armor/weapon material matters. I had 3 steel armored/armed dwarves before the first invasion hit and nothing that isn't steel armed/armored is a threat to me, at all, even though those dwarves started with terrible skills (and they are even now barely close to legendary in their weapon and with mediocre defense skills).
I'd much rather the combat was somewhat more dominated by skills, and perhaps weapon/armor quality (masterwork vs normal), rather then material. I know that's not "realistic" but really I don't give a damn about realism personally, compared to gameplay.