Biggest frustrations are actually frighteningly inane. You see, I can happily accept the pathfinding bugs, and the lack of the 40d merge, because I know with Toady, it'll take two or three releases tops before the worst of the bugs are gone.
The things that I'm irritated by are the ones Im not sure will get changed;
specifically, the channelling change and the huge increase in ore deposits.
With channelling, while I accept that digging a moat is an easy way of stopping any invasion, I feel the loss of functionality (and aesthetics, damn ramps flashing at me all the time) it introduces is too great a cost for what it does. Plus, it doesn't even really achieve it's original goal; its still possible to channel and then remove the ramps for a SLIGHT increase in time taken. In future releases, no doubt pathing improvements, jumping, and proper sieger behaviour will render a 1 tile wide ditch meaningless, but at present, a slight decrease in game difficulty is worth having the difference between channels and ramps.
As for the ore deposits, I originally liked them. I have to admit now though, they just get on my nerves. The huge increase in veins screws up low cost housing, looks unpleasant, and devalues all existing metals. It used to be that when I saw a vein of gold, I was ecstatic. Now I'm just irritated at the garish yellow streak through my floors.
I'll happily admit those are just my opinions, and other people may disagree, but I'd at the very least like to be able to choose which setup my fort had. (Incidentally, does anyone here know how to decrease the amount of minerals present?)