Standard-issue XCOM 2 is probably my least-favourite of the four different flavours of XCOM now available to us (i.e. including the Enemy Within and War Of The Chosen expansions), but that's a bit like saying I don't enjoy 29 degrees of heat quite as much as 26, 27 and 28 degrees. They're all great! Make it like that all the time, please. Only, y'know, without the heat-death of the planet. And, yeah, keep on releasing more XCOMs.
If you've avoided Firaxis' reimagining of The Greatest PC Game Of All Time (If You're An Old Man Like Me), XCOM 2 can be a rather full-on point of entry. On the other hand, it's currently free all weekend (and 75% off if you want to keep it forever), which is the easiest point of entry of all.
It's free to download and play from Steam until Monday March 25, and works on Windows, Mac and Linux. After that, the whole thing will lock up tighter than a feckless prime minister asked about their plan B - unless of course you pay. If you're thinking of coughing up for a time-unlimited copy, please do so before March 25, as the current 75% discount puts it at a truly bargainous £8.74/$14.99/€12.49.
Almost all the DLC's 50% off too, though to be honest the only one that's really worthy of merit is the wonderful, ridiculous War Of The Chosen expansion, now at £17.49/$19.99/€19.99. (Which still sounds like a lot for an expansion, but it is dozens, if not hundreds, of hours of heavily-remixed alien-bothering).
The Tactical Legacy Pack is the only other DLC humdinger, though sadly that's not discounted. Six quid ain't bad, though.