It is incredibly hard, and I am a long time Xcom vet from the very first game in the 90s (which was hard).
I got this on sale last fall and I literally cannot get past the early missions. The first one is easy on regular. From that point on though? Once you hit a "timed" mission I am done. I get that you have to take out the mind control sectoid, but even if you shoot him multiple times he might not go down, and heaven forbid if you get a bad roll, save and reload. In past games you sit back and plan your attacks, but with the time limit on most it is impossible to do that. Get into a prolonged firefight and not only are you badly outgunned, but you'll simply run out of time anyway.
I shelved the game honestly as it was simply kicking my butt.