It's Korea (Samsung Blue) vs Korea (Samsung White) in the first semi-final, and China (Royal Club) vs. China (OMG) in the other. One Korean team, Samsung White, is stomping the other and will be a huge favourite to win the final against whichever Chinese team wins. Last year a different Korean team, who didn't qualify this year (SKT-T1 K) won against Royal Club. The year before, Season 2, was won by a Taiwanese team.
NA teams performed strongly this year, but are still clearly below the best Korean teams. EU teams had their worst Worlds ever, having won season 1 and made semi-finals in seasons 2 and 3, but are still close to the NA teams.