Building a great API is a hard task. There are many pitfalls to avoid to succeed and since (hopefully) your API will be a dependency for many systems, you will want to try to hit it hard right from the start.
This makes a good API
In the talk Evan cites Joshua Bloch from Google who suggests that these points makes a great API:
- Easy to learn
- Easy to use - even without documentation
- Hard to misuse
- Easy to maintain the code that uses the API
- Powerful enough to satisfy the requirements
- Easy to extend
- Appropriate to audience
Ps. Also check out the lecture I gave at Berghs School of Communication on API design and product development. Ds.