Some poeple might not appreciate sharpshooters in xcom2 for one reason or another.
Man XCOM 2 will spoil you with that Sniper. After using that, then going back to Long War or Xenonauts, you'll have delusions of grandeur about what their actually capable of in the former games.
My love affair with XCOM 2 has rekindled my interest in both Long War and Xenonauts, which I still never beat (not for lack of trying). This sequence of events has led to me playing to the games in a cycle. Since I only play on Ironman mode (I enjoy it a lot more), I'll make it as far as I can in the XCOM 2 campaign, lose, switch to Xenonauts, get as far as I can, lose, switch to Long War, etc. rinse and repeat.
I'm assuming I'll beat XCOM2 first, because it seems the easiest of the 3 on "Normal". But man, I love all the games, they're all special in their own unique way:
XCOM2 - Definitely has the most streamlined and Arcade feel. The turn timers force you to do something quickly, the Conceal mechanic is a godsend, and the graphics and mechanics are the most streamlined of the 3. Also gives you the most feedback in terms of how you're doing in any given campaign, and holds your hand the most.
Long War - A tactician's wet dream. 8 classes all with 10 upgrades, and 3 choices per upgrade. This not including the 8 MEC classes, the SHIVS, or the "psionic" upgrades for the soldiers. All the possible combinations would probably be somewhere in the billions. Gameplay is starkly different from XCOM2. Where in the sequel, the start of the mission is a chance to cover ground as quickly as possible, in XCOM2 I've found that the best thing to do at the start of a mission is to
TEAM OVERWATCH for about 10 turns. Usually something will eventually walk into your party, igniting all your overwatches, and giving you a significant tactical advantage. This first alien encounter usually leads to many other nearby alien encounters, giving you the opportunity to fight the opponent on your turf.
I will admit, sloverwatch is an incredibly stupid mechanic, but reading this thread helped me see the value in it. Perhaps once you get into the MEC upgrades you can afford to play more aggressively, but in Long War, early on, one misstep into a horde of enemy aliens can spell your doom (so it's not worth it).
Xenonauts - Is definitely the most open-ended of the 3. This is for players that don't like having their hand held. The game gives you very minimal advice past the early text box here and there. There are no defined classes, and every element of the game can be tweaked by the player in degrees. In addition, the cover mechanics are a lot more flimsy and difficult to use, so your soldiers tend to be in great danger at all times. This is a game of extreme precision, where every tiny hex on the map matters to a massive degree, and the "2 turn" move mechanic of the aforementioned games is replaced with a much more complex "Time Units" meter, that can be brutally difficult to use. No Sloverwatch here boys. The aliens don't roam in patrols, and they seem to "hack" (aka have global map vision and always know where you are), so they will almost always make the best move possible relative to your actions. This means that you can't 'overwatch' forever, because walking into your team would be suicide. Sooner or later you have to venture into enemy territory, at your own peril...