100% AMAZING! We took a bus from Juneau to the glacier park - seeing many bald eagles along the way. Once at the park, they give you 50ish minutes to explore. If you walk very quickly, this is enough time to go out to Nugget Falls, which provides an excellent view of both the Mendenhall Glacier and the waterfall. We were also able to walk along the beach and see some glacier ice floating in the sea - which also gives you a great view of the glacier at the very left shore (looking at the glacier).
After the glacier, you board the bus again to the ship that will take you whale watching. On the ship are the captain (highly hilarious and also super knowledgable), a naturalist (who knew all of the whales' names and was able to point out many many whales), and another person who explains what you're going to see, the anatomy of a whale, and provides water and snacks (goldfish crackers, haha!)
We saw a ton of humpback whales. We sat for a good long while as they went around us in circles. They provide Nikon binoculars on the boat - so don't worry about bringing yours. If you have a zoom lens on your camera, you'll get some great shots if the whales are in the mood and the weather is in your favor. We got lucky with both!