NOACH – NACHAS RUACH
Noach 8.21 - וירח ה' את ריח הניחוח
The Zohar says that there never was or will be a ריח הניחוח like that one ever. R' Samshon R. Hirsch notes that it is the only time it says הניחוח with the ה'.
What was so amazingly special about this korban?
On a simple note, it was quite a unique korban. Noach took from ALL the pure animals and birds! Not only the classic korban animals and the turtledove or dove, but his korban included giraffes, deer and all kosher birds!
However, I would like to suggest, based on the medrash on the passuk before, ויבן נח מזבח - that Noach was מתבונן. He thought on his own and was מבין דבר מתוך דבר to build an altar and offer this sacrifice.
The mefarshim explain in the beginning of parsha that את הא' התהלך נח - Noach was led by the Din of Hashem. He did was he was told and commanded, in contrast with Avraham who took initiative and was an Ish Chessed who went beyond the law.
There is no such thing as a pleasant aroma for Hashem. The medrash actually notes that an Olah, with the entire animal being burned (and especially the cocktail of this one) gives of a very unpleasant smell. Rather the concept of ריח הניחוח and לעשות נחת רוח is to be understood as follows.
Ruach is always in motion. It is coming from one direction and hasn't reached its destination.
When Hashem has a will that does not depend on others for its fulfillment, it is instantly done and settled. But when He gives forth His will for humanity to fulfil, it is likened to ruach, something that has started and has a goal or target but has not yet been reached and is unsettled in motion. When Hashem's will is fulfilled, it is a נחת - a settling, of רוח - of His will that was in potential and finally came to be.
Here Noach finally made a 360. He achieved what Hashem WANTED. He thought on his own, to ascertain רצון ה' and that was exactly ratzon Hashem. Not just the korban. But Noach's approach! THAT was the ultimate ריח הניחוח!