I agree the meaningful tactical decisions are mostly the same (Flanking, suppression, explosives, snipers, use of smoke, cover, etc.), except served in smaller dishes, to use a food analogy.
But there is something more than just tactical combat. Even if with a good focused design you can have fun in very small scenarios with 2 corridors and a handful of simple rooms (look at Frozen Synapse, good game!), I still prefer something bigger.
It’s more a question of… how to say? Part immersion, part scope, part having terror missions feeling more epic than the normal ufo crashed missions, part exploration of the maps. The feelings of advancing through streets, parks and abandoned buildings, having to explore several floors in a house while I’m in tension. yeah “having to”, it may be a bad thing for people who want to cut to the meaty part, but for others it’s a good thing, “having to” explore empty areas without knowing if that street is really empty, or the aliens are in that part of the map.
edit
In a way, the X-com games are classics not because their cold but solid mechanics, but because they lend themselves to be very emotionally charged experiences. Shooting aliens in the dark, a soldier panicking when he see a friend die, confusing shots through the smoke, losing 1/3 of the squad while climbing down the transport, the feel when you clean half the map with the blaster launcher, searching aliens through a corn field or in a city through shops and warehouses, the feeling when one single chrysalids avoid your shots and transform everyone in chrysalids. It was all very moody, very emotional, and less like “just a turn based tactical game”. That’s chess.
So stuff that can affect the mood and tension is important.