I admit, I was a bit late to the X-COM party. The original game was released back in 1994, and at the time I was a child still enthralled by Doom. It wasn't until over a decade later that I would encounter X-COM as I began to explore tactics and strategy games more thoroughly; nevertheless, it left an impression on me that no other game since has been able to replicate.
XCOM: Enemy Unknown, Firaxis' take on the franchise, was released recently. I spent some time with the game (about 25 hours), and was impressed with the polish and effectiveness of its execution. However, despite its graphical and interface enhancements, it was unable to hook me in the same way that the original X-COM did. After some thought, I've concluded this isn't because it's an inferior game, that I'm nostalgic, or any other nitpicky reason. Rather, I think it comes down to the division between simulation and strategy and the different approach Firaxis brought to the game.
I am a very firm believer in videogame rulesets which apply in a universal fashion. My favorite games are RPGs, and generally speaking those games tend to revolve around rulesets which are explicitly statistical and defined clearly for the player as well as the non-player characters, environments and challenges on display. These sorts of rulesets are the real source of fun RPG gameplay in my opinion, because they are able to facilitate emergent play in a way that more fixed, non-universal systems can never emulate.
It doesn't really matter what kind of game you're talking about, either. Deus Ex remains possibly my favorite game of all time for its near-perfect blend of RPG mechanics and a global ruleset which governs the game world. Where most shooters rely on pre-scripted sequences and triggers to make the magic happen, the fun of a game like Deus Ex comes from interacting with systems of mechanics. It doesn't really matter what kind of genre a game is, though - the most fun for me have always been those which offer a set of open-ended rules for me to negotiate and play with.
Both of the X-COM games I've mentioned revolve around rulesets which, for the most part, equally apply between the player and the non-player aliens (at least, when in combat). They aren't RPGs as described above, but they both take from the same source - the idea that fun is the result of playing, not watching or "experiencing". Both games have consistent hit points, damage numbers, rules governing hit chances, a degree of simulated physics which informs how the environment can be navigated and interacted with, and so on. On the surface, they are very, very similar.
So why are these games so different? I don't think it comes down to the new XCOM being a simpler game, although in some respects it is. Rather, I think it boils down to the fact that Firaxis are not really interested in creating simulation-oriented systems, but game-oriented ones. That is, whereas the original X-COM had its tactical combat founded upon a set of in-depth interactions between the intrinsic properties of players, aliens and the game environment, the new XCOM treats the environment and the characters in it as pure gameplay objects designed with very specific functions in mind.
This is a bit of a difficult distinction to make, admittedly, but I think it is important to do so. In a game of chess, to continue the analogy, all pieces on the board have clearly defined functions and limited sets of abilities and interactions. In such a game, the difference between a pawn and a bishop is how much and in what direction those two pieces can move. Both have the same goal - capture all the other player's pieces - and the way they go about it is effectively identical. The strategy of the game is the result of most effectively employing the particularities of each type of piece, in such a way that accounts for and exploits the other player's pieces and moves.
The new XCOM plays much like a game of chess. There is a field with pre-defined points of cover for soldiers to hide behind, soldiers all have a set of abilities pre-determined by class, movement is limited to two moves and one attack per turn, and so on. Because of the way that these classes are defined, there are very clearly determined "right" and "wrong" ways to play them. The limited capabilities of each only accentuate this - a sniper is always a sniper, a support is always a support, and so on. Each is specifically designed to be use for a specific purpose.
The same generally occurs in the campaign on a wide strategic level. There are many specific methods to ideally game the research and base building elements. For example, panic rating is generally very easy to manage, especially if you hold off on deploying satellites to countries until the last minute. Upgrades are almost completely linear until the end-game - laser weapons are better than standard ones, which are both beaten out by plasma weapons. The way the story impresses upon the development of the campaign also means there are very clear objectives to accomplish at all times, and completing them in set order and by certain times is necessary not because of the evolving needs of the campaign determined by rules of cause and effect, but because the balance of the numbers is rigged to require you to play a certain way.
The original X-COM, by contrast, did not really play like a game of chess, or other traditional games with set scenarios and challenges to overcome in specific fashions. Rather, it featured a much more simulation-oriented ruleset. This was exemplified by the number of small details which the new game completely lacks. The original game allowed you to take advantage of these properties in creative and interesting ways; these weren't clearly defined in any play manual, but rather simply came about from how you engaged with the systems, and would often open up new possibilities at unexpected times.
For example, terrain destruction is still very much present in the new XCOM; however, now the feature has been solely relegated to certain weapon types, and only explosives are allowed to be precisely aimed. This reduces the number of options available and more clearly creates a role for explosive items that others simply cannot fill.
Similarly, the time unit system in the original game allowed for multiple types of attacks which "realistically" offered different upsides and downsides, as well as the ability to move, shoot or perform other actions in any order. The new game's two moves, one attack setup reduces options in combat and forces you to commit to decisions even if it does not really make sense why you can't fire and then move afterwards. The distinction between the original game's different shot types, with their upsides and downsides, and the new game's cooldown-centric design which clearly denotes that some abilities are simply more powerful than others and should almost always be used when available, is also obvious. In fact, many skills "unlocked" by leveling up soldiers actually simply fill gaps in your core set of options, which reinforce the feeling that they are being artificially denied.
The cover system is another thing that comes across as artificial. By clearly defining cover points, levels almost play themselves because the options available are made far more obvious to the point where creative thinking is no longer needed. Flanking, line of sight, etc. occur less as a result of your precision, timing and coordination and more as a result of you following predefined routes and highly engineered unit placement patterns. The entire combat system is basically designed around the use of cover, which only accentuates that feeling of a lack of options outside of the ones the designers specifically deemed acceptable in advance.
All this is not to say that the new XCOM is a bad game by any stretch. On the contrary, I had quite a bit of fun with it. However, it is obvious that Firaxis approached the game with a very different mindset - that of designers engineering a game in a classic sense, instead of an interactive toolbox that allows for a multitude of non-predetermined interactions. Considering their background with the Civilization series and the direction it has been headed, this is not surprising in retrospect - Civilization V also marked a clear step towards this "gamification" of the series with its greater focus on combat and downplaying of economics and diplomatic options.
X-COM was entertaining for me because it was unpredictable and exciting. Every mission played differently because the simulation-style rules allowed for so many interesting things to happen. Complex chains of cause and effect formed which hinged on every single small action. That sense that the game I am playing has already been predetermined, and that I am just picking a set of more or less binary outcomes from a very limited selection, robs the game of much of the depth and replayability the original is known for.
So while the original game is still going strong among many players even nearly 20 years after it was released, I simply cannot see the new XCOM attracting the same long-term attention. I don't even know if I'll be playing it a week from now.