StarCraft II Wings Of Liberty is a real time strategy game. It is a sequel to the critically acclaimed Starcraft: Brood war and since its release it has undergone quite a few changes. The graphics are largely left untouched, however some cosmetic changes have been done here and there, but most of the changes were done to the gameplay.
Who would have thought that after more than 10 years of development of this incredible game, there would still be room for more improvement. With the first few releases of StarCraft II Wings Of Liberty the gameplay looked just right, however a lot of players developed many techniques and a lot of different play styles that gave them an unfair advantage over their adversary. Most of the changes that have been done are only relevant to the online competitive part of the game. Many of the balance changes also changed the gameplay mechanics a bit. For example the infestor's cast animation was changed entirely and this gave the zerg player an opportunity to intercept the enemy units with its "fungal growth" ability. This was not possible in earlier versions. Another example of gameplay changes is the addition of a new upgrade for the protoss. You can upgrade the Pheonix's range to +2, and this changed the match-ups between Zerg and Protoss entirely.
One of the biggest updates was that Blizzard decided to make a free version of StarCraft II Wings Of Liberty. The free version is very limited, you don't have access to the campaign, the multiplayer ladder, but you can play online maps which mustn't be larger than 2 player maps. Basically you get a free version of 1v1, which in my opinion isn't that bad.
In any case, no updates have been done for a while now, although there are still players complaining on the official forums of imbalances and certain maps that are advantageous to some races. Most likely the developers are focused on the next sequel that is supposed to be released this year.