In all our trips, we only visited Tom Sawyer island twice, and never did the river boat. We have bad memories from our first time on Tom Sawyer island... in the blink of an eye our three young kids were missing, and then soon after grandma was missing. It all worked out but was scary for a bit. That place is a maze of paths and caves.
It was overdue to be replaced with something that more guests will use to enjoy, and to help relieve the crowding and capacity issues. I do like the Riverwalk/dock area and will miss that but am glad to have something more usable come in instead.