A good plugin does what it’s meant to do, and it does it well.
Business
- Performs the required function
- Is worth the price you paid for it
- Easy to use
- Integrates seamlessly
- Supported
- Popular
- Multi cultural
Technical
- Documented
- Updates itself
- Doesn’t hog the server; performant
- Is well written; respects how WordPress works
- Has potential: extendable, customisable