I know this is a slightly older post at this point, but the more I think about this new Nissa the less I like her. I thought this might be an interesting discussion.
I think this Nissa is good when she's able to win the game with her faux-craterhoof impression. While I think she's clearly worse as a big overrun than hoofdaddy (if you're ramping her out she might be giving as little as +3/+3, and she doesn't come with a free body– you need to have enough extra creatures lying around to kill the opponent after tapping your mana dorks), the fact that she's a pretty modal Planeswalker can make up for this weakness. She's definitely better than the other 7 Drop Green Walker (although maybe not better than Karn?)
So what's the problem? I don't think she is better than the commonly used 5 mana options, even when considering her modality. Cards like Nissa, Who Shakes the World, Wrenn and Seven, and Vivien, Monster's Advocate are all able to be used to their fullest extent when a player reaches turhn 5. While Nissa, Ascended Animist can start making 4/4s or blowing up artifacts or enchantments on 5, I am not convinced that is better than the high synergy outcomes the other three common 5s can provide. You really need to be getting up to 7 for her to be fantastic in my view, and you need to have enough forests and spare creatures for that ability to pop off. Compare that to Nissa, Who Shakes the World, who can immediately start ramping a player to the moon the turn she comes into play, Vivien, who can be a combo and draw engine, or Wrenn and Seven, who has interesting graveyard and land synergies and makes powerful scaling tokens .
Essentially, I think Nissa, Ascended Animist is cool and unique, and when she works I think she's a bit beating. However, I think she is just one of several interesting options for Big Green Walker, and isn't necessarily the best. I think Nissa, Who Shakes the World still probably holds that title.
What does everyone else think?
Simply put, I disagree!
Making a 4/4 as a + ability (!) is pretty good in regards to using her to her "fullest extent" on turn 5. A 4/4 is meaningfully bigger than a 3/3, and you'll get a 5/5 the following turn if Nissa's not disrupted. The other 5 MV walkers don't have that same escalating danger, and are less necessary to kill on site for opponents if they hope to survive.
World-Shaking Nissa doesn't start ramping the turn she comes into play unless you're in a scenario where Phyrexian!Nissa is entering with a 6/6 beater, and Wrenn and Seven can be downed by a shock after placing a treefolk. I get you on the lack of neat synergies, but even ignoring the fact that Nissa, Ascended Animist is a three-way split card, the average case scenario for Nissa is much better at 5 than the competition. The scenarios where you've built your deck in a way to maximize the other walkers AND where that comes together exactly on five mana are, from my spitballing, dramatically less common than scenarios where you're able to squeeze more value out of the Ascended Animist by skipping the Phyrexian mana in her cost. The powerlevel may not be as interesting, but it's real, and it's more robust imo
I don't have any interest in cubing her (for reasons outlined earlier in the thread), but I do think generically she's the best MV5+ walker in green all the same. I would personally advocate for cubing Nissa, Who Shakes the World over her because she makes for a more dynamic cube environment. Raw power on a card-by-card basis is not the ideal I'm personally maximizing for, but if you are...Phyrexia never sleeps.