For my projects, I can produce with LLMs a codebase that I'd be proud of, but it requires extensive use of the plan mode and nagging anytime the implementation looks much more complex than the feature at hand requires.

Anytime I tried spec driven development, it produced total garbage, the problem is that the model usually swings too far, if they write unnecessary complexity, a nag about it and you risk it code golfing, this problem across 100 lines of specs and you're guaranteed it will swing too far on some segments you just wanted X slightly more than Y (usually for me it was reliability dropped for better readability since # users = # developers = 1)

Another thing I dropped is steering implementation design too early, start with the goal and nag in the direction you want, it works well for me but might not work well for big complex codebases.

For now I love LLM coding but I'm sure my opinion will change if I have to review code from a developer that does the 1 prompt = 1 PR without looking at the code jutsu.