I have visited the Baha'i Holy Places twice now, and both times I've had limited access to the gardens in Haifa. Really just bad luck.
The gardens are beautiful and are one of the top attractions for tourists visiting Haifa. At the top of the gardens, you get a great view of the entire city and the harbor.
The view from the bottom of the gardens at night is spectacular and it is a great place to eat in the evening as well.
Make sure to check before you arrive as to the operating hours of the garden and if there are any holy days or other special events going on. On my first trip I could only take photos through the gate. On my second trip, I could only visit a limited part of the garden.