I've painted up some extra miniatures for both the human and alien sides, to make the original scenarios better-balanced.
First up are some Elhiem Figures "armoured fed troopers", used as medium-armoured X-Com operatives. These are incredibly good miniatures that fit well with plastic 1/72 miniatures. Hopefully they are part of a trend popularizing 1/72 scale science fiction.
This is one of the armoured troopers compared to a Caesar ultra modern miniature. You can see that they fit together perfectly in terms of height and proportions.
Another comparison shot with a Caesar miniature and the Elhiem carbine trooper.
I'm thinking of using these medium-armoured X-Com troops against the original snakemen, and give them better armour and weapons ratings than the poor initial tech-level humans.
To get a bunch of easier opponents for the humans at early tech levels, I painted up some sectoids. These are Rebel Minis alien grays, and even though they are designed for 15 mm, they can fill in as child-sized aliens for 1/72. The only modification I did was to add some wrist-mounted plasma pistols since the originals were unarmed.
I'll see if the humans do better this time. The sectoids, just like in the computer game, are significantly weaker than humans and only have plasma pistols. Hopefully this will give the early level humans a fighting chance.