Must say lot of the scenarios feel a lot harder than the original game. I suspect it may just be my being unused to enemies warping in (I lost half a team in Exodus when a shitload of Shredders and a Reaper dropped onto us, in the middle of a retreat from what seemed an essentially UNKILLABLE SECTOPOD HOLY SHIT IT DROPPED THE COMMANDER, BOOK IT!)
Assault was interesting but perhaps the most familiar, the only thing to catch me off guard was when I somehow forgot that setting a fireteam on overwatch to take the zombies staggering down the hall was a HORRIBLE idea when they were armed with only laser weapons.
Cataclysm was perhaps the most bizarre, hilarious, if the most unfair feeling. I started out next to peculiar Dr. Faust, I'd no idea what to do with all the needles he has in his house, so while we decided it was a good idea to take everything. Another pair of the troopers attempted to lead the family to safety... until their path was blocked by a crysalid. At which point, I and my soldiers shit our collective pants and ran back into the house to regroup with the now 'armed' pair of troopers leaving Faust's.
I decided to throw the unstable compound after the crysalid charged through the window and implanted a fellow in the living room. The only survivors were a crysalid, a trooper who bled out in the next round, Faust, and Timmy (both of whom had been outside.)