Good code is a lie imho.

When you see a project as code, there are 3 variables in most cases:

- time
- people / human resources
- rules

Every variable plays a certain role in how the code (project) evolves.

Time - two different forms: when certain parts of code are either changed in a high frequency or a very low frequency, it's a bad omen.

Too high - somehow this area seems to be relentless. Be it features, regressions or bugs - it takes usually in larger code bases 3 - 4 weeks till all code pathes were triggered.

Too low - it can be a good sign. But it should be on the radar imho. Code that never changes should be reviewed at an - depending on size of codebase - max. yearly audit. Git / VCS is very helpful here.
Why? Mostly because the chances are very high that the code was once written for a completely different requirement set. Hence the audit - check if this code still is doing the right job or if you have a ticking time bomb that needs to be defused.

People
If a project has only person working on it, it most certainly isn't verified by another person. Meaning that only one person worked on it - I'd say it's pretty bad to bad, as no discussion / review / verification was done. The author did the best he / she could do, but maybe another person would have had an better idea?

Too many people working on one thing is only bad when there are no rules ;)

Rules. There are two different kind of rules.

Styling / Organisation / Dokumentation - everything that has not much to do with coding itself. These should be enforced at a certain point, otherwise the code will become a hot glued mess noone wants to work on.

Coding itself. This is a very critical thing.

Do: Forbid things that are known to be problematic in the programming language itself. Eg. usage of variables in variables, reflection, deprecated features.

Do: Define a feature set for each language. Feature set not meaning every feature you want to use! Rather a fixed minimum version every developer must use and - in case of library / module / plugin support - which additional extras are supported.

Every extra costs. Most developers don't want to realize this... And a code base that evolves over time should have minimal dependencies. Every new version of an extra can have bugs, breakages, incompabilties and so on.

Don't: don't specify a way of coding. Most coding guidelines are horrific copy pastures from some books some smart people wrote who have no fucking clue what you're doing and why.

If you don't know how to operate on people, standing in an OR and doing what a book told you to do would end in dead person pretty sure. Same for code.

Learn from mistakes and experience, respect knowledge from other persons, but always reflect on wether this makes sense at this specific area of code.

There are very few things which are applicable to a large codebase on a global level. Even DRY / SOLID and what ever you can come up with can be at a certain point completely wrong.

Good code is a lie - because it can only exist at a certain point of time.

A codebase should be a living thing - when certain parts rot, other parts will be affected too.

The reason for the length of the comment was to give some hints on what my principles are that code stays in an "okayish" state, but good is a very rare state