Most likely the Celebrity ship will be Millennium (the one we sailed on); HAL might be Westerdam or similar.
Millennium built 2000, 91,000 tonnes, 2170 pax
Westerdam built 2004, 82,000 tonnes, 1964 pax.
Very similar.
Millennium Class is our favourite Celebrity ship design.
Westerdam seemed a bit more cramped.
Dress code or lack thereof is the same for both companies.
You will not find a library worth it's name on any Celebrity ship.