No it's not X-Com, but keep an open mind and you'll enjoy it.
The story takes place on Earth, after two events known as Twilight and Nightfall. Starting May 24, 2004 a giant alien vessel released massive clouds of toxic spores onto our planet. They multiplied so rapidly that the entire sky was blackened; this was the Twilight. As the spores fell to Earth they clogged streets, bodies of water, and smothered people to death. During what would be latter called Nightfall, most of all human life was wiped out. The few that did survive soon formed the Council of Earth, weeks after the spores had died, and plotted their counterattack. You are placed in charge of the Council ordered to find a way to destroy the Reticulans ("Greys"), responsible for the heinous attack. The story is strong, and the ending is pretty good. Halfway through as well, events change to put immense time pressure on you, all the better for the story. It ends up being a lot more than your traditional "alien invasion" plot.
The game is also significantly darker and more serious in tone than pretty much any other X-Com style game out there. Your main enemies are Transgerents, utterly disgusting mutations of what was previously human. In addition the Reitculans aren't a very pleasant bunch, with their bases usually decorated with human corpses. The atmosphere is enhanced by these terrible enemies and the believable environments, giving the game a more emotional layer than is to be normally expected. The emotion doesn't run extremely deep, but it's there.
Story and atmosphere aside, the game is still divided into two sections; Strategic, and Tactical. The Strategic side of things has been greatly simplified, and manages to move much more quickly, while still retaining "strategy".There are really only four things you do on the geoscape: participate in random missions, choose which bases to build, determine research and manufacturing, and of course intercept UFO's and investigate their ruins.
Missions are the primary driving force of Aftermath, and the feature that gives it much more variety than the rather limited (but great) gameplay of X-Com UFO Defense. Every so often missions will pop up all over the world, each with various goals. The most important ones are base captures, which expand your territory and influence, but there are others including, but not limited to capturing live specimens, attacking alien bases, conducting reconnaissance, or eliminating prowling alien patrols throughout your territory. Since you're a "special forces" unit, you don't have to participate in all of the missions. The game assigns a "impact" and "urgency" rating to each missions; the less important ones can be delegated to the general Earth Armed Forces. This is a wonderful improvement as you no longer have to slog through 100+ missions if you don't want to. Of course, it's still beneficial to participate in missions, and it its possible to overwork the regular grunts. All of this in addition to the traditional UFO interception, gives Aftermath a lot of variety.
As you capture bases, you have to decide what you want the base to specialize in. Rather than choosing the entire layout of your base you merely choose from three types; Military, Engineering, and Research.
Military bases are where your squad rests and recuperates, use radar to detect enemy UFO's, and launch interceptors. Since your squad travels by a rather slow chopper, it's important to place these bases on the outlying edge of your territory so you can quickly react when necessary.
Engineering bases contribute to your manufacturing capability. The more engineering bases you have, the faster you build items. Just like X-Com, various weapons you research can only be built, not bought or sold (a system missing from Aftermath anyway). Here you'll also create various improved versions of armor from shielded alien armors, to heavy mech-like suits.
The third base type, Research, contributes to how fast you discover new technologies. The more you have, the faster research goes. The tech tree is very expansive, and the large amount of enemies guarantees that alot of it will be autopsies alone.
There is one more base type, but to reveal it would be a spoiler. Let's just say that rapid research to attain these bases is required or the planet will be destroyed.
Besides the general Base System, we should talk about your squad. UFO: Aftermath uses a RPG-like system to track the progression of your team. You only control one squad, and it is comprised of a total of seven members. As these members fight in battles and gain experience they level-up and gain various attribute points. Each soldier has multiple skills, but rather than raising skills they raise the determining attribute (which in turn raises the skills). In addition to this system, you have the option to train team members in various professions assuming they meet the prerequisites. For example if a soldier's dexterity and agility are high enough, you can invest in Sniper training. It's a good system and one of the joy's of the game is watching your lowly squad turn into a heavily armored killing machine.
The simplified strategy elements work really well. There is thinking to be done in what bases should be prioritized, especially early on when your bases are limited. The flow and pace are fast with the source of new weapons coming from liberated bases (and there are a ton of weapons). The squad system is also deep, and you have more control over how soldiers develop. While long time X-Com fans may be disappointed by the streamlining, there's no denying that things move a lot quicker and you'll be able to fight more battles. Besides, any future X-Com remake could learn a thing or two from Aftermath's variety.
The tactical side of UFO: Aftermath uses a real-time pausable system, called by the game as SAS (Simultaneous Action System), which is essentially a hybrid between turn-based strategy and a RTS. You plan out all of your soldiers actions, which are then carried out when you unpause the game. In order to help things along, the game also automatically pauses for certain events such as spotting an enemy, in order to give you time to cope.
I'm usually not a huge fan of these systems, but it works. When compared to game's like Brigade E5, UFO's system is noticeably smoother and less clunky. SAS also allows for much more realistic combat situations, such as two characters killing each other simultaneously, something that's impossible without a suicide attack in traditional turn-based games. The system is not perfect. The game pauses far too often, and their aren't enough auto-pause options in order to tweak the system to your liking. In the end, a SAS system isn't smoother than TBS at all, in fact it may be even more choppy. Still, there's no denying that it greatly speeds up battles and is more realistic, even if it tends to get annoying in larger skirmishes.
Graphics are the most disappointing aspect of this title, but they're quite decent. While it is an older game, geometry is rather basic and most characters tend to look slightly polygonal. Textures, and lighting are passable and help compliment the splendidly designed environments. There's extremely dense cities of all different styles, thick jungles, sparse forests, mountains, and even more. As I said earlier, enemy design is extremely creative and atmospheric so the art direction is top-notch. Unfortunately, game is locked in at 1024x768 an embarrassingly low resolution which looks horrible on my 24" widescreen monitor.
Sound is passable. The music is solid and helps contribute to the atmosphere. The geoscape tune is catchy, as it should be given that you spend so much time staring at the globe. Sound effects are rather good, especially firearms which are suitably powerful. Alien noises can't live up to their designs though. Voice-acting also leans on the corny side, not even being charmingly stereotypical (like JA2 or Silent Storm).
Those two issues aside there's a very solid game here. Some will be turned off by the simplicity, or the real time combat system, and other will decry it as "not being X-Com". Newsflash, it's not trying to be...give the game a chance. The balance is great, maps are of high quality, and after you adjust to the SAS system...it grows on you. If you're looking for a fast paced strategy game, with sufficient depth, UFO:Aftermath is worth a look. The interesting story, and the strong atmosphere are great bonuses in addition. I would thoroughly recommended to all fans of strategy, especially tactics.