As with anything, features can depend on intended usage.
Beyond the basics of weatherproofing, battery life, onboard storage capacity, the convenience of battery changing, mounting options, etc. I'd consider:
- Night vision - a lot of animal activity happens at night, so a good night vision camera is key
- Sensitivity - do you only want big animals, or anything that'll trip a basic PIR switch?
- Timer mode - to conserve batteries/storage - do you only want the camera to operate between certain hours (sunrise/sunset periods, for example)?
- Video - do you want moving as well as static pictures?
- 3G/4G connectivity - automatically upload content to cloud servers?
- Security - do you need to protect the camera from passers-by/rockfalls/hangry bears?
- Environmental impact - does the design/colouration/placement of the camera adversely affect subjects or the environment in which it's placed?