Setting of the 1st game was kino.
XCOM 2's setting sucked at the start, the saturday morning cartoon villains of WotC proved the writers had no idea how to write an XCOM game.
Supposedly you're the last scraps of humanity fighting the overwhelming space fascist government who has actual cosmic horrors at their disposal.
The gameplay had your squad of demigods mowing down the entire alien invasion without breaking a sweat. Any semblance of the horror aspect that defined the originals, and imo was still present int XCOM2012 was gone.
However the main issue is the gameplay, it ironically starts out great, but deteriorates as you get more powerful:
In the initial game your soldiers are inaccurate, and even at the best of times you have trouble wiping a pod, forcing you to think about counter-play and make contingencies when a shot misses. The game literally threw a mind-controlling sectoid at me in the first mission, and I thought the devs are willing to bust the player's balls, and force him to strategise. Literally that was the only instance of MC used in the entire campaign, after that the sectoids just raised zombies.
As I got more and more powerful, I got a ton of items and abilities that allowed to reliably wipe the enemies in a single turn and land the majority of my shots, or evade retaliation should some of them survive.
The alien variety literally doesn't matter, basically almost any composition of soldiers can handle any kind of aliens, the only strategy being - shoot it until it dies.
The pod system doesn't allow you to gain map awareness, flank your enemies, set up ambushes, since if you happen to discover a new pod while positioning your soldier's you are fucked.
The procedural maps and timers mean that there's very little use in exploring the maps, or using their layout to your advantage, as you're constantly moving anyways.
TLDR: The game's systems prevent it from having any deep gameplay.