After upgrading from Hudson 1.334 to 1.336 (as well as upgrading six plugins), I get

java.io.IOException: Dependency analysis-core (1.0) doesn't exist
at hudson.ClassicPluginStrategy.loadPluginDependencies(ClassicPluginStrategy.java:374)
at hudson.ClassicPluginStrategy.load(ClassicPluginStrategy.java:237)
at hudson.PluginManager$1$3$2$1.run(PluginManager.java:202)

followed by

java.lang.NullPointerException
at hudson.PluginManager$1$3$2$2.run(PluginManager.java:218)

and then all hell breaks loose as no descriptors can be found for anything:

java.lang.AssertionError: class hudson.plugins.xvnc.Xvnc is missing its descriptor
at hudson.model.Hudson.getDescriptorOrDie(Hudson.java:900)
at hudson.tasks.BuildWrapper.getDescriptor(BuildWrapper.java:194)
at hudson.model.Descriptor.toMap(Descriptor.java:595)
at hudson.util.DescribableList.toMap(DescribableList.java:120)
at hudson.model.Project.getBuildWrappers(Project.java:117)

If I go to Updates and manually install analysis-core and restart, then everything is back to normal. But the update manager should have noticed that there was a missing dependency from one of the updates and forced me to install that dependency before I restarted the first time. And a missing dependency for one plugin should not cause all the others to fail to load.