After collecting strategies on the internet I found a easy way to beat it on Classic: Squadsight Snipers.

That's basically it. You use your 2 first months to babysit your Sniper until he gets Squadsight and use him to kill almost everything. It's boring, it's slow but it's safe and reliable, and if shit hits the fan you can always retreat your Sniper to the Skyranger and get the fuck out.

Honorable mention to Shredder Rockets Heavies. Outside Snipers they'll be probably the only people in your missions killing stuff before the Sniper get big. 2 Rockets means (at least) 2 kills at the start of the game when everybody has 4 HP max, and usually beats your 30% chance to hit with guns.

The game has some nice, but unusable, ideas... Shotguns are super risky because advancing means bringing more aliens to the party. Shotguns should been a sidearm for Assaults, not a replacement for the rifle... though I love the sound and the animation.

I hope they fix this stuff on the 2nd game and I hope you have a bigger squadsize and a more streamlined interface. I could move and kill 12 soldiers faster on the original than I can do it with 6 on XCom.

And yes, I'm a Rikka fan.