How does one query the binary blobs in an event store?

One of the much touted benefits of event-sourcing is that it makes debugging an application's execution easy because one has the complete log of every event. But if the events are generally stored as a binary blob with limited metadata, how are they interpreted in a useful way?

Does one generally build a tool that can query the event store, deserialize the events, and then reserialize them in a human readable format? What if one wants to filter on a field not included in the metadata (but in the binary blob)?