I am a thread derailer, so I'll post here, may help others to make up their minds.

Biggest difference between the UFO:A? and X-Com series is that the battles are Real Time with Pause instead of Turn Based. You also cannot field the huge teams you could in X-Com, but usual team is 4 to 7 people, depending on game, research and mission.

On to more specifics.

Base Management.
In UFO: Aftermath, base management is quite simple. Bases can be Military (allows helicopter to launch from them), Research or Engineering. There is a 4th type that will be available later ingame, so no spoilers from me. More research bases mean faster research, more engineering mean faster building of things. Military ones are only useful for launching, but you'll still need quite a few of those.
In UFO: Aftershock, each base you have has a limited amount of building sites, where you can build specific facilities. Depending on facility type, different research and manufacturing becomes available.
I can't quite recall how UFO: Afterlight handled base management, since it has been too long since I last played it.

Planet division.
Earth (or Mars) is split in sectors, and each sector is a potential mission site. You can either wait for a mission to pop up, or you can try to start a mission yourself. Specific sectors are designated as base sectors, and grabbing those will give you an additional base to use. If you lose said sector, you also lose the base (obviously).

Soldier training.
Your soldiers have 6 stats that are random when created, with a value of 1 to 7. Each time your soldier levels up, you can increase one stat by 1. They also have access to specific trainings (sniper, scout, soldier) that have different stat requirements. So you will have to designate specific roles for your soldiers, and you won't be able to have Jack of all trades (well, you could, but you'll probably get slaughtered). Your soldiers are also killable, and if they die, they are dead. In UFO:AM and UFO:AL, recruiting soldiers is hard, since there is either a limited amount of them or they only appear after a certain amount of time has passed. So no rookie kamikaze tactics. In UFO:AS, you can recruit as many as you want, assuming you have good standing with the different factions.

Combat missions.
The thing I liked most in UFO:A? was the fact that you didn't need to kill all enemies on the map. In elimination missions (and most of them will be elimination), you need to kill 90% or so, though nothing prevents you from killing all of them. You are also able to capture aliens alive, and a few missions require you to do that.
Other than elimination missions, you also have extraction (reach point of friendly unit, escort it to exit), kidnapping (identify specific hostile unit, capture it, escort to exit), civilian escort (escort group of civilians to exit) and I think there were also assassination missions (identify enemy, kill enemy). There are also a few more story missions, but I'll let you find those yourself.

Research and Development.
There is quite a bit of it in all games, though the most fun of it is in UFO:AS and UFO:AL, since they allow for weapon modification. Things like scopes, silencers, bayonets, grenade launchers etc are (eventually) available, and your scientists will dream up quite a few new toys as the game progresses.

Enemies.
The enemy types are varied, and just as you start getting used to them, the game will throw new enemies on you, forcing you to reevaluate your tactics and your squad's loadout. Weapons that may have worked before may no longer be able to scratch the new enemies, so you'd better have something else with you, or you'll be forced to retreat and lick your wounds. Autopsies are always available, assuming you do manage to bring a corpse back, so you will learn how to deal with the new enemies. But of course, that means you have to kill one of them first.

Conclusion.
The games are fun. UFO: Aftermath is the weakest of the three, UFO: Afterlight has the most mods and customization, but I personally prefer UFO: Aftershock the most, since I do find some things in UFO:AL as too much. But the character personalities in UFO:AL are excellent :)


Apologies Lou for hijacking the thread (again).