Is that really restful though? If you need that many parameters to specify which resource you mean, you lose pretty much all of the benefit of a restful architecture.
GET vs. POST is a question of whether the request is intended to change state. Using JSON for a query is nice for preserving structure (e.g. nesting a Boolean expressions, not needing PHP-style array notation, etc.) but it doesn't change the idea that it's a GET request which can safely be repeated without affecting server state, may be cached for other clients, etc.
