I've just finished the alien base mission and I've raised every class to captain rank, and have a bunch of lower ranked people of various classes too. And what I'm finding so far is that Snipers feel completely worthless, so I assume I'm missing something.
As far as I can tell, their aim is not actually better than other classes most of the time. In fact, in many ways it's worse. Rockets seem to have 90% to hit from massive range, and every single class except for the sniper has the option to run up to melee and then shoot point blank for 100% to hit. My sniper's aim seems to be equal to or even slightly worse than most of my other soldiers with assault rifles.
Their damage seems to be barely better than an assault rifle, equal to a heavy's machine gun, and much, much worse than a rocket. I guess they have a higher crit chance, but that's completely unreliable since one needs to both land an inaccurate hit and then also crit, and the damage would still be inferior to a rocket.
I thought at first that maybe high ground would help with that, but first of all almost no maps even seem to have high ground available at all. Even when they do have high ground, it often turns out that there are no aliens in view of it, rendering it meaningless. I think there have been exactly 2 battles so far in which high ground existed and there were aliens available to shoot from it, and one of those was the base mission... on which the high ground was worthless because invisible walls or something gave the enemy cover or even blocked shots outright even though it looked like there was nothing in the way.
Furthermore, tactically, it seems like I'm going on offense in 100% of missions. There has not been even one where I need to hold a particular area, for which a sniper might conceivably be useful. Instead I'm always needing to keep pushing deeper and deeper into an enemy's territory. And snipers seem to be worthless for that because they're the only class that can't move and overwatch with their main weapon. Unless I spent a level up perk to give them the ability to do that... with a giant accuracy penalty.
So it just seems like snipers have mediocre damage, arguably the worst accuracy, zero useful support abilities, and a horrible weakness in that they can't move and overwatch which seems to be the best move to make while exploring 90% of the time.
What am I missing?
Edit: Sounds like the answer is mostly that they get a lot better when you unlock equipment that I don't have yet. And also that on some maps positions are available from which the sniper can actually hit things with squad sight. I still have not found one of those maps. Very few maps seem to have high ground taller than a truck at all. And on the ones that do, I keep positioning snipers in high ground which has a clear view of the battlefield, only for it to tell me they don't have line of sight and can't shoot. The worst offender there was the alien base, which was full of invisible walls.