since "product" is the item I would do:

GET /product/recommended?user_id={user_id}

the "type" of products you want is a sub-set of all products (recommended). For differentiators I think using params is good. You can then do something like:

GET /product/recommended?user_id={user_id}&rating=5

etc...

Seems clean to me, but also is just my opinion.