I've heard very convincing statements proving that it is impossible for this to get much worse than three mile island, and I've heard very convincing statements proving that it is likely to be worse than Chernobyl.
The end state of this seems highly uncertain. The best case scenario is that going forward, everything is going to work fine. They'll start cooling the tanks and the reactors and there will be no more leaks. In this case, the total damage will be severe, and the plant will not be used again, but the area around the plant will be fine to use in a few weeks.
Worst case scenario is that they fail to keep a reactor or storage tank cool, the hot fuel breaks containment, and there is some kind of explosion that spreads debris over a wide area, contaminating a region for centuries. Luckily most of that would be the pacific ocean, which just means that part of Japan's most abundant food source would be both poisoned and unpolicable. I'd expect it would be necessary to check all fish caught in the region with a Geiger counter before sale. Yes, your seafood would not only need to be mercury-free and dolphin-safe, but also rad-neutral.
A medium potential is that containment is breached but there is no explosion, merely contaminating the plant and the immediate locale, and the groundwater, and the coastal waters.