By Spring 4.x it felt like the ecosystem had learned the value of staying close to vanilla Java - annotation-based configuration meant that there would be a (Java) reference to any class that was instantiated by Spring, constructor injection meant that there was less need for Spring-specific lifecycle methods like afterPropertiesSet() and it was more practical to write "dual-use" classes that could be used with or without Spring.
Whereas for me Spring Boot has the same feel as the bad old days of early Spring 3.x - lots of magical constructs that were impossible to understand unless you knew all the Spring specifics. A Spring Boot application will behave completely differently based on just which libraries happen to be on the classpath - the exact same code might start up a tomcat server when run one way and not when run another way - and has a whole host of new Spring-specific things that you have to learn if you're going to understand how your application is behaving.
Whereas for me Spring Boot has the same feel as the bad old days of early Spring 3.x - lots of magical constructs that were impossible to understand unless you knew all the Spring specifics. A Spring Boot application will behave completely differently based on just which libraries happen to be on the classpath - the exact same code might start up a tomcat server when run one way and not when run another way - and has a whole host of new Spring-specific things that you have to learn if you're going to understand how your application is behaving.