The first season is a little slow but introduces the entire world pretty well. The second season ramps up the story and has one of the best arcs I've seen in awhile (maybe not that good, but still good). Watching Season 3 now, but it's pretty disappointing so far. The story dropped considerably, and the humor is getting a little stale. Still want to watch it to the end, though.
Sorry, but you're being misleading and incorrect. Soul Eater is a single season comprised of 51 episodes; it is not four seasons of 12 to 13 episodes.