I'd say one of the big annoyances I've encountered while building applications with the last few versions of NextJS is the increasingly tight integration with the built-in server. The world of Node servers is pretty well-established, with documented interfaces that the major server platforms all implement and support. Simple stuff like res and req in the context and what those objects contain. With each release NextJS breaks a bit more of those interfaces and replaces them with approaches that are very specific to NextJS and pretty unintuitive to anyone who is used to building servers in Node. I'm talking about stuff like handling response codes (the notFound parameter you need to return to get a 404 from getServerSideProps is a particularly egregious example) or redirects. You are presented with what looks like a standard interface, but doesn't fundamentally actually work anything that interface.

Decades of working in this industry have taught me to value interoperability, modularity and standardization. I love the idea of a framework that makes SSR easy, and the idea of static site generation, and a router that uses the pages approach where each file is a route is handy in some cases (though very clumsy in others), but all of those a different things and aren't really something I need a single monolithic framework for. I may want one or some or none of those things based on what project I'm working on. If NextJS makes it harder to pick and choose what I want to use, or makes some features contingent on using other features I don't really care about, I'm going to start looking really hard for an option that gives me more choices.