All the experts have been writing a LOT about the problems with the Fukushima Daiichi reactors. A 9.0 earthquake is pretty much impossible to predict, and there's no such thing as 'too safe', so complaints about design, safety, and planning seem fairly pointless. But we are learning some hard lessons, and slowly finding out how bad this is.
It's apparent now, four weeks after the quake, that TEPCO both doesn't know the full extent of the problems, and has been unwilling to disclose all that it does know. Reactors 5 and 6 seem safe, and 4 seems to not be the focus of concern now. Reactors 1,2, and 3 are being cooled still by pouring more water in. The #2 containment vessel is assumed to be breached, and contaminated water is probably leaking into the sea. The #1, 2, and 3 fuel storage pools are still steaming or smoking. #3 may also have a leak in containment, as pressure is not building inside the vessel.
Vegetable and dairy products cannot be shipped from the region due to contamination. Radiactivity assumed to be from the accident site is found in tokyo, China, and as far East as New England. This is bound to raise worldwide background Radiation levels.
Overall, what I read in the first week was to expect all this, to watch for breached containment, and ultimately expect to see the entire facility off-limits, with reactors 1-3, and probably 4, entombed, and 5&6 unusable. You can write off Fukushima Daiichi as a total loss, with massive cleanup costs over the next decade and continuing maintenance costs for the foreseeable future. That's 40 years minimum. Watch for building a new seawall, interceptor wells, transporting soil and everything else possible out of the plant, and then letting it cool down for 10-30 years.
The single biggest question seems to be whether the fuel in 1 & 2, and maybe 3, has melted, pooled, and probably has reached criticality in small quantities. The fear expressed by at least one former design engineer is that the fuel will eventually melt through the concrete at the bottom of the secondary containment structure and leak out into the ground. This would cause massive contamination both in ground and sea. No idea where the fuel pool would eventually end up, but imagine having to dig a 200 ft hole to start scooping up this hardened, glassy mess. Covering the site to avoid dust and debris being released into ther air. Where do you put this? How much is still how hot? Robots? You won't be using people to run the machines, as their expected work cycle would be measured in minutes. The lessons of Chernobyl are being re-learned.
This is a case where the worst-case scenario is largely coming true. It was bound to happen.