The NCLA cruises are popular because they're the only ones that allow for a cruise of 7 days that will hit all the major ports in Hawaii. Having said that, it WILL be a very different cruise experience than sailing the PG (or any other Regent ship). HAL might be closer in terms of quality but they'll be doing either one ways from the mainland to Hawaii or back or doing those 2 wks roundtrip ones (I think that HAL might not do the roundtrip ones but I haven't checked in a while)

This might be useful:
http://www.luxurycruisetalk.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=19;t=000092

If you do NCLA, be prepared to lower your expectations somewhat and plan on spending money at the alternative restaurants instead of eating in the main dining room or planning on eating off the ship.

Let me know if there are specific questions regarding NCLA.

Masaki