I agree, the streamlining of the rules from 4E -> 5E is a big deal, perhaps the single most important difference is the fact that 5E is simpler to play.
Ask ten people and you'll get ten different explanations for what's wrong with 4E. For me, the problem was that combat is time-consuming. The time it takes to resolve a single combat encounter might be one or two hours! I really enjoy the combat in 4E, but I feel like this kind of crunch has narrow appeal.
For other editions, earlier and newer, it seems more natural to just ignore rules you don't want to play with and end up with a simplified game very naturally. With 4E, it felt like you couldn't do that with the combat system.
Ask ten people and you'll get ten different explanations for what's wrong with 4E. For me, the problem was that combat is time-consuming. The time it takes to resolve a single combat encounter might be one or two hours! I really enjoy the combat in 4E, but I feel like this kind of crunch has narrow appeal.
For other editions, earlier and newer, it seems more natural to just ignore rules you don't want to play with and end up with a simplified game very naturally. With 4E, it felt like you couldn't do that with the combat system.