Slingshot is a DLC - or minor expansion - for last year's hugely successful turn-based strategy game, XCOM: Enemy Unknown. It shouldn't be confused with the absolutely massive and far more significant expansion, Enemy Within, out in November. Slingshot is an altogether modest, though far from pointless, affair. On console it will also be included with Enemy Within should you wish to wait for that release.
Slingshot makes a number of modest changes to a game of XCOM. It gives you a new character, a former Triad operative who quickly becomes a Lieutenant in your organisation. Starting a new game with Slingshot installed sees you get this character quite quickly, which can accelerate early-game progression. This has good and bad points. On the good point, you'll get him promoted (and thus access to the six-man squad upgrade) much earlier than normal. On the bad side, having a character of his level in your squad will also trigger the arrival of mid-game bad guys earlier than you normally would encounter them, which can cause a steep challenge if the new character is then injured or killed and has to sit out missions.
As well as a new character, there are also three new narrative missions. These missions see you taking down an alien battleship which is about to attack China. In the first mission you have to extract the new character and his intel on the alien ship. In the second, you have to install an alien homing device on a train to lure the ship into an ambush, and in the final one you have to storm the alien ship and capture it. This results in a significant early-game boost to XCOM's acquisition of new technology. It's all good stuff and can have a discernible impact on an XCOM playthrough. In particular, the much earlier unlocking of alloy rifles and other high-level weaponry (which usually are unlocked too late to make any major impact on a campaign) can make a big difference in how the endgame plays out.
For a modest cost, Slingshot (***½) does add some nice new features to an XCOM replay, though its feature set (but also the price) is dwarfed by the incoming changes from Enemy Within. For those who are already addicted to the game, Slingshot adds some welcome replayability.
Note: Slingshot is included as part of Enemy Within, so do not try to purchase this is you already have Enemy Within!