VideoGame Afterlight
Afterlight is much more in X-COM's style then it's predecessors. You lead a small group, no more than twenty at most and only seven in the tactical missions, to defend the planet...which happens to be Mars. The elements of the game most closely resemble Apocalypse, with a split soldier/scientist/tech personnel system, but there is one noteable absence: interceptions. Enemies do not arrive by air typically in Afterlight, and even if they did conducting major repairs on your lone aircraft isn't possible, so it's much too valuable to risk that way.
Whereas Aftermath was short on actual need for tactics, Afterlight will respond reasonably well to your efforts to play it as if it were really a squad-based game. In dealing with the heavier enemies things can feel a bit Napeoleonic (how many squad-based games are there where you form a firing line that often?) but splitting up into fireteams of two or three for an X-COM style sweep is both quite possible without dying horribly and even frequently useful.
Afterlight offers things the other games did not. Cenega layed off the ridiculous weapons selection for this game, opting instead for an X-COM-like simplicity and the possiblity of two tiers of upgrades and a few different ammo types, allowing customization to the task without much sorting through a mountain of guns. You can also command aliens for the first time, your old Reticulan foes or even "true" Martians. And you can build your own robotic drones to offer your troops heavy support in the field; not as impressive as X-COM's tanks or SWS since they don't stand up to fire well, but just as powerfully armed. You can also recover damaged Martian drones from the field and eventually repair them, though your own offer greater versatility and protection. As if in answer to the prayers of the beleagured commanders of all the X-COM games, there are night missions...and real honest to god night-vision or thermal imaging gear for your troops, letting you fight in darkness with confidence for the first time. There is a variety of sensors to detect your foes with as well, letting you track them by anything from their metal weapons to their scent.
All in all, Afterlight is a worthy successor to Apocalypse or the other games of the X-COM series, and I highly recommend it.
VideoGame Aftermath
People talk about how the Afterblank series are a spiritual successor to X-COM. This is...somewhat inaccurate, when speaking of Aftermath. Allow me to explain.
Aftermath contains quite a few X-COM-like elements like interceptions, geoscape/tactical, and the alien invasion premise. However Aftermath plays fundementally differently. Your interceptors, for example, are semi-disposable. There's no money-management aspect as you represent more or less the last of humanity under arms. Weapons selection for your troops is much more varied, though you'll find that this doesn't add terribly much to the game.
Most of all, the tactics are very different and somewhat dumbed-down. Playing Aftermath the same way you played Enemy Unknown or Terror From The Deep is possible against the lesser transgenant enemies or in the late game when you're packing gatlings and enhanced plasma rifles and god knows what else. But usually, you will find that the advantages of concentrating your team together outweigh the advantages of dispersing them; there are no hostiles with grenades in Aftermath, and you will need the concentrated firepower against Reticulans for most of the game, outweighing the dangers.
Aftermath is much more forgiving than any of the X-Com games as well. You can make mistakes. You'll lose at least fifty aircraft a playthrough and more likely a hundred plus, something impossible in an X-Com game. There's actually a lot less scope for tactical engagements in the game, and the only opponents it would matter against, the Reticulans, it really makes little difference except for remembering to put the guy with the CAWS or flamethrower on point.
If Enemy Unknown and Terror From the Deep were too tough for you, Aftermath might meet your needs. Apocalypse is a closer cousin to Aftermath, and so those who enjoyed it might also enjoy Aftermath despite its major departures from any of its cousins. Overall though, I find Aftermath difficult to recommend strongly; it's eminently playable and it's well-made, but it's just not as engrossing as the tactical X-Com games were, primarily because it lacks their incentives to force you to think.