Jake and the designer in charge of balancing Legend talk about the differences between Legend and Impossible in this video
Hmmm, the guy balancing Legend doesn't seem to have a clue how to even play the game, lacked the rhythm and instincts of it I found. Probably "video chills" but within 10 mins starting up he managed to make cringe worthy mistakes pretty much every single turn and yet came out completely unscratched at 4 vs 5. Not very good PR wise but I can "see" what they mean by "Legend is different from Impossible". Never really played Impossible personally as I found anything above Classic just boring and forcing you to just abuse the system but some folks who lived by it might indeed find the whole thing a tad too simple. That said, "mod will fix it" I guess and it's still early.
More worrying (though it IS a month old preview build and these last couple months are where lots of balancing happen) is the remark Beagle made at some point about the entire thing snowballing hard and fast (on Legend with only the first couple month of the game playable), which apparently was why he kinda modded shit a bit.
Overall the entire thing look sleek though (obvious bugs aside, but there nonetheless). Aside the raw improvements you can expect from a sequel, tons of little shit I think are really cool (character pool, sight indicator, waypoints, queued overwatches, etc) and the more PC focused interface seems more fluid. I'm a sucker for character customization/progression and that bit looks quite nice from what I've seen.
The apparent new dynamic of the tactical layer seems to offer players a wider variety of worthwhile play-styles, the lack of which is what annoyed me the most with XCOM:EU as snipers/scanner were just too abusive and powerful (and the core of anyone playing above classic from what I've seen). I very early stopped using the sniper class due to that obvious abuse potential but that made even classic much harder, though more fun (for me that is). More available turn limitations also seem to push you constantly and restricts non-stop over-watch traps for hours, which is a good thing in my book as well. Feels like the new EU4 mechanic that locked troop movements half way, to prevent obvious abuse that everyone was somewhat forced to do as it was insanely powerful and yet annoyed everyone.
Dynamic maps look fine so far as well, should enhanced dynamic play and replay-ability a lot, especially since they'll probably release some "chunk" DLC/FLC as well.
Geoscape also looked more dynamic with constantly tons of shit to do, choices to make and whatnot, rather than just wait for stuff to complete and aliens to do something. Might allow for good specialization of a play-through, and allow to recover if something went to to shit or something. Also fits well with the story of being a resistance instead.
So far really looks like a good sequel to Firaxis XCOM:EU/EW. Still a Firaxis XCOM:EU/EW but once you accept what that means (and can find some fun in it), then it seems it's only improving and adding couple new twists on it. Even the preview appears polished and made with attention to detail as well and there should quite a bit of mods done on it which never hurts.
Clear buy so far, though not gonna pre-order or anything yet. Hundreds of hours in EU/EW and this looks only better so well worth the money.