A while into the project, my team and I were responsible for delivering a subcomponent within the system. We did so with extreme prejudice to only using actors at the very edges and entry points where a bit of asynchronicity was required. But everything within the service boundary was just plain old Java. This was the easiest to understand and maintain part of the system, as attested by another team who we handed over the entire codebase to. Guess which part had the least bugs? Most extensible?
I don't know if akka has improved since then, but the debug workflow was such a departure from the normal way of doing things on the JVM it was enough to put me off and then steer clear of it in general. There are definitely other patterns and libraries I would reach for first.