The truth is out there. And unfortunately, the truth is that the X-Files Collectible Card Game isn't very good.
To be sure, it's not an unmitigated mess like so many CCGs. It's attractive, it has an exemplary rule book, and it's relatively easy to get Mulder and Scully (listening, Decipher?). It has some intriguing mechanisms which don't merely Magic. It's a shame it's a bore to play.
The cards themselves are a juxtaposition of the do's and don'ts of graphic design. Each different type of card has a distinctive layout while retaining a unified look and feel thoughout the card set. They're interesting to look at yet organize their information clearly and effectively. Sadly, this is undermined by the choice of an excessively small and difficult-to-read font. You'll need good lighting and good eyesight to read these. The quality of the photographs which form the centerpiece of each card is spotty. Some are crisp, but many are blurry or otherwise substandard.
The X-Files is essentially a dressed-up version of Clue. Each player secretly chooses an "X-File" at the start of the game, each of which has four attributes. To win, you must use deduction and logic to identify your opponent's X-File by narrowing down those attributes. This is accomplished by playing Site cards and investigating them with your team of agents, earning the right to ask your opponent a yes-or-no question about his X-File.
There are dozens of X-Files to choose from, so narrowing the field isn't a trivial process. There is absolutely no value in owning more than one of any particular X-File, though, and they're mostly common cards. Players will quickly rack up useless multiples. Worse, there was a card distribution problem in the first print run of boosters. Many boosters consisted entirely of just two types of cards, some of which were duplicated within the same booster. I opened one 15-card booster which had nine X-Files in it. Then I opened a second and found the same nine in that one! The distribution has supposedly been fixed, but there's still no use for duplicate X-Files.
Perhaps the most interesting mechanic in the game lies in the division of many cards between the Bureau and the Conspiracy. Rather than taking the Star Wars or Netrunner approach and having players take opposite sides in the conflict, players take on both roles at once. You're the FBI agents while trying to discover your opponent's X-File, and the forces of darkness while trying to stop your opponent from discovering your own. You have two separate pools of points used to pay for cards of the appropriate type. FBI agents generate resource points used to put Bureau cards into play. The clever part is that you discard Bureau cards to earn their cost in Conspiracy points. Instead of keeping not-so-useful Bureau cards in your hand, you can convert them to points needed to pay for Conspiracy cards. Slick.
Where the game falls short, though, is in the interaction between players. Maybe our decks were just not constructed right (and if so, that's another problem— if fun decks are hard to build, beginners won't get into the game), but it was very difficult to impede the opponent's progress. Adversaries and combat cards allow agents to tussle with the conspiracy, but combat can be a rarity in which case such cards aren't particularly useful. "Bluffs" can make it harder for your opponent to successfully investigate a site, assuming you get bluffs which are playable on that site. And that's where the game's big problem seems to be. Each card has a number of keywords associated with it which dictate which other cards can affect it. And there are a lot of different keywords, which makes it quite possible to have a hand full of great but inapplicable bluffs.
Now let's flip it around for a second. As the investigator, you rarely know what bluffs might be waiting for you at a site, so you have no way to prepare for them. You just have to cross your fingers and hope your cards can handle whatever the conspiracy throws at you. So on each side of the game, there's little way to know what you'll be up against and thus little chance to make informed strategic decisions.
X-Files is a good try, but its misses overshadow its hits.