After 15 games with the expansion, here are some early comments.
(1) Combining the whole package (new board, sanctuaries, whispers and spirits) seems a bit overwhelming at first. The game is less predictable and it becomes difficult to assert that a move is intrinsically better than another given the larger range of things that may come next. Sometimes I had to "let it go" not to burn my brain and just accept to play suboptimally. The very best players will probably find the game has gained some new depth, but most of us may find the luck factor has increased a bit, as you cannot control everything at the same time.
(2) The sanctuaries are disappointing. Freezing a hex and 4 tiles is actually a big cost, if you consider the land points and animals you could have done with them. And the reward is not that high, given that good players will pick animals carefully and build their game to finish most of them by their own. Maybe I have not found the right approach yet, but so far I tend to simply ignore sanctuaries if I want to play competitively with the expansion.
(3) In the opposite, the whispers are very strong. Their required land patterns are very easy to match, and scoring 4 to 10 points is actually very impactful and above the win/lose gap in most games. Besides they create their own lot of combos with animals (however they also add extra cards to the deck so decrease the probability to draw the classical combos between animals: if you play with Pulse and Crescendo together, it is much harder for a pingouin to find a manta or a bee to find a fox...).
(4) The new boards are very fun. Set aside the new scoring rules, the simple thing to have new shapes is sufficient to renew the game quite much and break your routines. At this stage, I consider these new boards are the best addition from Crescendo. You can totally enjoy to play a classical game (no whispers no sanctuaries) on these boards.
(5) A thing that I find a bit annoying is that the illustrations of the sanctuaries and whispers tend to be a bit more abstract than those of the animals, so we may have a hard time referring to them in the forum. When I say "squirrel" everyone knows which card I am talking about without ambiguity. But if I say "wooden house" it could refer to several different sanctuaries. And "flowers" to several whispers. Maybe we will have to define an official naming convention. Or we will use terms such as "the green-red sanctuary", which is practical but lacks a bit of poetry...
Curious to read your own views if you gave it a try already!