General antonyms:
* Liberal
* Open
* Free
* Unrestricted
* Expansive
* Permissive
* Loose
* Flexible
More specific antonyms:
* Generous (if referring to restrictions on resources or opportunities)
* Inclusive (if referring to restrictions on participation)
* Unbound (if referring to restrictions on movement or action)
* Broad (if referring to restrictions on scope or range)
* Unconventional (if referring to restrictions on thought or behavior)
The best antonym will depend on the specific meaning of "restrictive" in the context you're considering.