Ok, this is a lot of stuff that will have to wait until assorted stability and features are done, but it is stuff I have been thinking about and want to put out there for consideration.
Right now, in my experience, every game is pretty much the same, and generally risk-free. Once you master food production and handling immigrants - and avoid silly mistakes with flooding - the only real danger is the demons of the pit. I haven't played on elephant maps yet but I already find it pretty easy to get across the cave river and set up my main base on the far shore by the first winter; that seems like a pretty effective escape from elephants (or pretty much any wildlife issues). Also, there are no meaningful constraints on how or why you excavate. Aside from the stone properties (soft stone tunnelling faster) mentioned in an earlier thread, ore quantity and type should be such a constraint - you should want to seek it out - but right now it's so plentiful people can just dig out according to preplanned layouts and pick up so much in passing they don't need to look for more (iron and coal being the exceptions).
Every map is also the same in the sense that every map has the same ores and stone types everywhere. Games would be a LOT more interesting if this was varied. You always need limestone, coal, and iron somewhere on the map, but the rest of it should vary - different games should play differently depending on the prevalence of different types of ores. Maybe the map has mostly silver, and you make lots of silver weapons and armor and coins, and you're good against supernatural enemies like werewolves, and you're legendarily rich, but need to import your picks from caravans. Maybe you find lots of tin, and end up building all your doors and furniture out of it (it would be better than raw stone) and trading huge amounts to the caravans in return for weapons. Or you've got the ores for brass, and can either go with a weapons and armor strategy using the copper and be independent, or make brass tradegoods and be dependent on the caravans for equipment. This would add a new and interesting challenge to the early-middle part of the game, and would make the various fortresses qualitatively different.
Actually, it would be even MORE interesting if there were different ways than just steel bridges to get across the lava. But they'd be just as hard to manage. Maybe bridges made of crystal glass with a dose of magic, or specially treated obsidian, or using aqueducts and channels to divert part of the river over the lava - a wide area, and only the very center would be walkable. Or special equipment or heroes or something. In Age of Wonders the dwarven Firstborn were immune to fire, and got sent across lava all the time; that was cool.
Then there's rock types. It doesn't make sense that one particular area of mountain has ALL those types of rock all together. The basic rock types should be one of just a few types. Different areas on the world map should have different primary rock types, and different secondary rock typse, and other rock types that simply aren't found in that area at all. Same for the light and dark stone - maybe a given map has a decent amount of marble and onyx, but no jet or obsidian at all. This might not seem like a particularly meaningful change, given that the only constraints imposed by rock types are limestone being needed for steel and obsidian needed for obsidian shortswords - but it can be used for something much better; making search patterns more sensible. Right now, when you go looking for a hard-to-find ore - usually coal or iron - the standard thing to do is to make a giant grid of rectangular tunnels. That's kinda silly and looks ugly and wastes a lot of time. What would be a lot more interesting would be to make the veins of a particular rock type be much larger, AND to associate them with a particular type of ore. It wouldn't be absolute, but your odds of finding a certain ore would be much better if you find a vein of the right rock or stone and follow it. This would make the different types USEFUL as opposed to their only effect being slight differences in caravan prices, and your dwarves' preferences.
There's just gotta be a better way to go looking for ore than digging up the entire map in rectangular grids.
Next, opposition. You get frogmen popping out of the river, lizardman random attacks, and so on. Ok. Right now it's just an annoyance. One comment I saw in the SA thread was that a guy who reached the demons had a herd of war dogs that had very efficiently dealt with every single other threat up to that point. I believe it. That shouldn't be possible. Dogs are light infantry/cavalry types at best, they should be ok for the first couple years and for softening the enemy up (and maybe providing a screen for your marksdwarves) but there needs to be many more steps of threat before the endgame. Maybe while tunnelling you break into a goblin cavern kingdom, or find a frogman village along the shores of the cave river, or a big nest of creepy-crawlies somewhere. Maybe a lizardman army shows up and lays seige from the river (an unexpected direction). Maybe a dragon - or three - climb out of the chasm and head for your treasury, incinerating everything and everybody in the way. Stuff that makes you NOT just tunnel madly eastward to see what you find with no risk until you reach the lava. The Underdark is _dangerous_. You're supposed to be building a fortress and getting into serious trouble, not laying out a shopping mall.
Also: I haven't had a chance yet to play more than a year and a half on a haunted map, but the wildlife didn't seem at ALL more dangerous than in my current game, a "Calm" area. Actually "Calm" has unicorn herds, which have already massacred half of one caravan; in the Haunted game I just had skeletal groundhogs to deal with (and skeletal macaques, which aren't much tougher than raccoons). (There were some skeletal wolves and cougars too but they never bothered me.) If I just haven't played long enough, ok, but I would expect that by the first winter there would be a lot more pressure from the undead and so on. Maybe after a couple years a vampire count shows up with an army of thralls and tries to kick you out. Maybe your dead dwarves rise from their graves all at once and attack their former comrades. It should have the player be constantly - from the very first day - on the edge of their seat and paranoid, and right now it just isn't.
The game is supposed to be an "inevitable march to destruction". Ok. Fact is, that sounds like a fun challenge. But it is fun if and only if there's lots of different ways to die - Yet Another Stupid Death, but with an entire city. Right now, there's flooding, starving, and the demons. There needs to be lots of others, that have a good chance of truly destroying the fortress, at every stage. Minor random encounters aren't any sort of challenge.
Basically, there needs to be a LOT more variability in games aside from the precise locations of ore veins and the shapes of the three barriers. (Though that also could use some more variability. But it's not as important an issue as the rest of this.) This is, in a lot of ways, a Roguelike strategy game; the great strength of the roguelikes is the randomness, and how every game is different. There needs to be stuff in the game, choices presented to the player, that MAKE it different, and challenges beyond "how do I feed my growing population". All the maps I see of people laying out the same basic type of giant rectangles and just steamrolling eastward tells me that's not present yet.
I understand this is "just an alpha" and the main thing right now is bug stomping and implementing features. Not a problem. I certainly will keep playing - even as-is the game is damn fun. But before getting too far into feature creep like armies and world conquest, issues like these have to be addressed.