With EJBoss, you drop your bean in the deploy directory and off you go. That is very important since the EJB specification speaks to the needs of the deployer. EJBoss really goes the extra mile to deliver on it and make the deployer's life easy. Other EJB servers pay lip service to the needs of the assembler and deployer. However, their true focus is only on the developer.
Scalability is another big issue.
This is where the EJBoss container architecture will shine. This is very important because on the Web, these servers will need to scale in production. If you find the information in this interview of interest, check out the authors' presentation at the O'Reilly Conference on Java. NextGen is the code name for EJBoss1.0. Like the rest of the industry, I relied heavily on classic compilation and non-dynamic stub and proxies for the EJBoss implementation.