Most people who play Starcraft enjoy competing with others online. This may be because the AI is pretty weak, and you are able to defeat them once you know their strategy. One of the initial hardest tasks was to compete with 7 other races in melee. However, the difficulty depends on the map. It is possible to defeat all the other 7 (random) races in melee if you hunker down by blocking a chokepoint, or go inside one of the enemy and hunker down behind their minerals. This strategy works on most of the normal maps. The most difficult (and seemingly impossible task) is to defeat all 7 random enemies in an island map. Island maps are those that have your base initially in an island, and you must build drop ships and planes to reach the enemy. In this case, there has never been anyone who has achieved the task of defeating all 7 random enemies in melee. For regular maps, you can see how it is done by visiting
http://www.edepot.com/game.html and downloading the replay (protoss versus 7 random enemies in melee). Perhaps one day someone will have a successful strategy, but for now, the AI is very strong for 1 versus 7 in melee on island maps, and is impossible to defeat.