First off, air combat is great - I mean, finally - this has always been a very important part of these games and it irked me that XCOM 2012 pretty much ignored it. Here it's way more important, plays better, and has a much better consequence spiral.
I wanted to like this game - I have hundreds, if not thousands, of hours in the original X-COM games. I've finished TFTD on superhuman ironman. I've played a ballistics only UFO Defense... I even made my way through XCOM Interceptor...
♥♥♥♥ this game though - and for one simple reason - the Aliens always know where you are. And this isn't the X-COM: EU type of alien squadsight where if they see one troop, they can see all your troops. This is where if you are within range of an alien, even one that's never looked outside the UFO, it triggers a special AI. This is the kind where if you have a wall between you and an alien, the alien will be facing you through the wall.
Remember how in TFTD there would be those little closets where aliens would get stuck because of a pathing bug? And to kill that last alien you'd have to either eat up its reaction fire with rookies or blow through the walls from another direction? Well, this is half of the aliens in this game. And you can't blow through the walls. UFO breaches, depending on the layout, are either brutal or tedious. Most of the time the aliens will just sit behind the door in their command center, full TUs, waiting to reaction fire as soon as you make a move. And that's nothing compared to alien base assaults.
Jesus effing Christ - the beginning of the assault are fun - about a third of the aliens on the map will make their way to the LZ and try to push you out. The next phase is classic XCOM - carefully make your way to the control room, removing opposition as you go. The last phase is just mind-numbing tedium - 1/3 of the aliens in the base are sitting in a single room, barely moving so they can keep their TU high for reaction fire. Problem is that there's something like a 60% chance that if they hit your fully armored guys, they will kill you in one hit. They, on the other hand - take 3-5 hits, on average to take out. Now, add in the lovely 'Dread' effect and half your team will have 30% of their TUs removed. Just 'cause. It's like they combined the worst parts of all the XCOM games - Alien PSI spam, Lobstermen Bullet Sponges, XCOM 2012 projectile/cover dynamics, Apocalypse AI camping - and they put it all into a single room.
Then we can talk about LOS issues - they are everywhere. The number of times I have gotten shot (or have shot) through a wall is ridiculous. Or aliens shooting through solid obstacles from the fog of war. Or sitting in the middle of a roof and having an alien along the wall of the building be able to hit me. How about trying to throw a grenade over a knee-hgh wall, only to realize that you don't *throw* grenades so much as you fire them in a direct line from your chest.
Moving past the map issues, the way ballistics work is just broken. In the original X-COM, you shoot a bullet, it will fly in a straight line until it hits something (Wall, scenery, alien, back of your team mate's head) or it goes off the map. It's simple, it worked - your accuracy percentage was your chance to hit a target at 20 tiles, that accuracy determined the size of the cone the bullets leaving your weapon would travel. The game didn't care what you were shooting at, just put the bullets in that cone and they did what they did - whether it was boring a hole through a house or taking down a floater. Here, you have a) a chance you'll hit the alien (XCOM 2012) and b) a chance to hit anything in the way. (XCOM 94)
Let's say that you're shooting at an enemy with a LMG. There's a bale of hay between you and the enemy, but you know that your LMG can shoot down that hay bale if you get 2-3 shots into it. So, you force target the alien and the first 3 rounds of your 10 round burst do indeed destroy the obstacle between you and the bad guy. You expect to see the 7 remaining bullets proceed to kill or even just supress the alien on the other side. Unfortunately, the remaining 7 rounds just *poof* disappear, stopping where the hay bale used to be because that chance to hit an alien is determined before the first shot is made. That's the XCOM 2012 binary hit / miss calculation ♥♥♥♥ing everything up. Even if you have a clear path between you and the alien, the bullet will still disappear at the alien's square and you'll get a *miss* text pop up over the alien's head. It won't continue past them on these occasions, possibly hitting the explosive barrels on the tile directly behind them, just another *poof*. That game said you had 95% chance to hit that alien, and even if your bullet had perfect dead-center trajectory, that 5% will kick in and eat that bullet.