At the same time, this is the worst nuclear accident since Chernobyl, and in some respects worse than Three Mile Island (TMI). At TMI, they managed to avoid a hydrogen explosion; in this case, Japan had hydrogen explosions that destroyed much of the buildings at two reactors (though not the steel pressure vessels around the reactors themselves).
At TMI, there was only a very modest release of radiation. Here, you have at least one worker reportedly suffering from substantial radiation sickness and scores of people whose exposure is being carefully assessed and clear signs that there has been some significant release of radioactivity, including cesium and iodine (though reports seem to conflict as to how much). At TMI, one reactor’s core was destroyed. Here, it appears at least two have suffered fuel melting, a third reportedly has exposed fuel, and others are facing serious loss of cooling.