Well, I finally completed this level start to finish (and to other finish), so I think it's about time I give my two cents on this level: it's good. It's really, really, good.
Petals II is a nice-looking, yet challenging level that definitely lives up to its predecessor. (Although to be honest, I hadn't even played Petals I until a few weeks ago when the new patch for it dropped. Despite being in the KS community since around 2011, it must have missed my radar somehow.)
I can tell there was quite a bit of time and care put into each of the areas, both graphics-wise and challenge-wise. I feel this level's difficulty toes the line between Hard and Very Hard, and while I was able to complete it all the way through, I won't lie and I'll say that there were quite a few screens that gave me some trouble the first few times around. It's a beast of a level, but if you're an experienced KS player (or platformer fan in general), it is definitely worth playing.
I will admit that I did have to peek in the editor twice to get the secret ending (once to find the artifact in the hive, and twice to find the GC entrance in the garden. To add insult to injury, I now remember that I stumbled upon that in my first playthrough but had to find it in the editor before I even remembered that it was even there. D'oh.), but oh man was it worth it! The ending was short, but very sweet and definitely worth the journey back. Like Purple Ink said, it really adds another dimension to the level's story and makes the experience that much sweeter after the trials you've faced. (Also, good lord, that one set of screens in the castle with the fire and the switch took me quite a while to beat. Gosh.)
All in all, this level proves that Talps has still got it. I will be adding this level to Juniverse as soon as I can!
EDIT: Forgot to mention, but I actually quite liked the chase section/"hive", as it were. Quite challenging, but quite fun, imo. Keeps ya on your toes.