Log Horizon, much like Sword Art Online, features people being stuck in an MMO. However, Log Horizon happens in the middle of the game, when an expansion launches and players find themselves transported to the video game world.
Much like Sword Art Online, Log Horizon has a bunch of characters that make up its cast and are all different classes in the game. The leader character Shiroe is more of a tactician and behind-the-front-lines player though, unlike Kirito, who would lead the charge.
Log Horizon is also paced much slower than Sword Art Online. Action scenes occur less often and the story seems to move much slower. However, the battles seems to be more complex and strategic in Log Horizon.