Having built an app recently with Spring Boot, I admire them for trying to make Spring as simple to get up and going as, say, Rails. And it's certainly better than Spring was on its own.

But in my experience it's still an enterprise-grade Frankenstein's Monster, and the developer experience is pretty bad compared with other frameworks I've used. If I was doing something on the happy path, it mostly worked. But the moment I tried to do something slightly different than they expected, I was 20 frames deep into Spring stack traces trying to puzzle out poorly written Spring code. I've done a lot of Java, so I could eventually emerge triumphant. But it was a giant time suck. Looking back on the project, we estimated we could have done it in half the time using something like Rails or Flask.