Never done much Spring, so I don't have a lot to compare to. But ...

I'm not a massive fan of using annotations in concept, because they obfuscate what's taking place. Unlike in (say) Python, where annotations are effectively functions wrapping the function they annotate, in java they're more akin to a customisable preprocessor. Obviously I do use them, liberally, because that's the way things are done, but I'm not a big fan. And using any modern framework relies on these a lot.

Micronaut gripes -

1. It works great until it doesn't, and you have a special case, and then you have to dig into source to figure out what on earth is going on.

2. Keeping up with latest isn't always easy, micronaut 3->4 was a huge effort.

3. For all it's called micronaut, the produced packages are pretty huge.

Serverless-specific gripes -

1. What I'm receiving isn't really an http message over a socket. It's an AWS gateway event with everything already read and packaged up. So there's no reason that (for instance) I shouldn't access the message body in a request filter, because I don't give a crap about the jetty server-loop being non-blocking.

2. Startup time is terrible. And when I managed to get a native compiled version to actually run, it got worse. A lot of this seems to be down to hibernate, but there's a big gap between startup and any logging from the framework at all. We've tried a bunch of stuff to remediate, so far with little success.

In general I think that serverless is such a different paradigm from a long-running server that approaching it from the point of view of "how can we make this the same so developers who've never thought outside of the spring-like box can still be productive?" was wrong from the outset.