MLS and American playoff systems in general are not bad. From an interest standpoint, they simply move some end-of-season drama from the bottom of the table to the middle. I am glad they're not the only model, though. Variety is the spice of life.
Closed-shop American leagues also make a debatable but not insane tradeoff of fewer fans getting top-flight sport in their towns, but more fans getting a legitimate bite at the apple for a championship.