I am not familiar with this company, but there are many out there that do a wonderful job with Alaska, from both the cruise and land standpoint.
The value of doing a cruise + land tour is that Alaska is not only huge, its various areas are quite different from each other. On a cruise you will see just the Inside Passage area - spectacular, to be sure, with lots of wildlife (mostly bears and marine mammals/birds). Its climate is milder than most of the rest of Alaska, and tends to be wet - a nontropical rainforest. Interior Alaska is somewhat drier, and will substitute moose and caribou for the marine life; the land tours will concentrate on a portion of the interior, usually the corridor between Anchorage and Fairbanks, including Denali National Park. Both areas of Alaska are must-sees, in my opinion (I have been to both).
The John Hall company may be a good start, but do yourself a favor and consult with a good travel agent in your area - preferably one who is an Alaska specialist, or has experience in that area - to see what your other options are, both in types of travel and in cost, before you commit.