HAL is indeed more formal, but not so much as one would think. A couple of years ago, they simplified the dress code to two classifications - formal and smart casual, which you can read about HERE
. Jackets are not required on the non-formal (smart casual) nights. Most of the gentlemen will wear anything from dockers with a golf shirt to slacks with long-sleeve button down shirt, no tie. Formal can get pretty formal, yet the gentlemen will not be out of place in a suit/jacket/tie, and the ladies will be just fine in a cocktail dress or silk pantsuit.
That all said, the itinerary may make a difference. Which HAL cruise(s) are you considering, and how many nights are they?