Without doubt, Sukkos is filled with more mitzvos than any of the other holidays - from the sukka to the arba'as haminim practiced everywhere to the nisuch hamayim and arava in the mikdash (later universalized by the early prophets (Sukka 44a-b)). Interestingly, the Talmud (ibid. 43a, 44a) derives these mitzvos from fundamentally different types of sources. The primary mitzvah of the four species is derived from an explicit verse, "And you shall take on the first day, the fruit of a beautiful tree..." (Vayikra 23:40). Their taking in the beis hamikdash is derived from a derasha on the verse, "And you shall rejoice before Hashem for seven days" (ibid.). Chazal understand the phrase "before Hashem" as a reference to the mikdash. The mitzvah of arava and nisuch hamyaim are derived from halacha l'Moshe miSinai, "pure Torah sheb'al peh". To be sure, all of the mitzvos are always informed by a combination of Torah shebichsav and Torah sheb'al peh, but the conglomeration of all the different combinations - straightforward pesukim = pure Torah shebichsav, dersahos = a combination of the written and oral Torah, and halacha l'moshe misinai = pure Torah sheb'al peh - in one festival is certainly notable.
Homiletically, perhaps we can suggest an insight highlighting a central feature of Sukkos which serves as the culmination of all the festivals of Tishrei. Our relationship with HaKadosh Baruch Hu is first and foremost one of created to Creator, or servant to King. This is fundamental to our status of total dependency - both in our initial creation and our continued existence - on Hashem Yisborach. However, Hashem has chosen to partner with man in creation. One of many passages which indicates this partnership is the statement that "there are three partners" in the creation of a new child (Nidah 31a); the parents provide the body and Hashem provides the soul. In reality, there is an unequal partnership, as the parents are merely utilizing all of the tools G-d granted them combined with the complex rules of the natural world He created. Nonetheless, our Sages reflect Hashem's will by referring to this as a partnership. Similarly, Rav Chaim Volozhin (Nefesh HaChaim 4:10-11) quotes the Zohar that Hashem created the world with speech, and those who study Torah continue to create the world with speech - "if not for my eternal Covenant, the laws of Heaven and Earth would not have been formed" (Yirmiyahu 33:25) which the Talmud (Pesachim 68b) interprets to mean, "would cease to exist."[1]
One of the most far-reaching areas of human partnership with the Divine is in the realm of Torah shebe'al peh study and analysis. The opinions of mere mortals - even though their modus operandi is to merely use the Sinaitic-principles of Torah analysis to arrive at an educated theory of "what Hashem would have said about this case had he revealed it at Sinai" - become part of Torah. "Eilu v'eilu divrei Elokim Chayim" (Eiruvin 13b). Rav Chaim Ya'acov Goldwicht zt"l, founding Rosh HaYeshiva of Yeshivat Kerem B'Yavneh would often highlight this concept through Kiddush Hachodesh where the Beis Din's ruling is binding even if mistaken or even if deliberately in error (Rosh Hashana 25a). He would also often quote the Talmud Yerushalmi which indicates that on the thirtieth day of Elul which might be declared Rosh Hashana down below, the heavenly court gathers with its myriad prosecuting and defending angels ready to commence, but Hashem awaits the declaration of Rosh Chodesh on earth. If it is not forthcoming, the Supreme Judge dismisses the court and declares that the Day of Judgment will have to take place the next day since Beis Din did not sanctify the month on the first day! With this endowed power, man is not just passively acted upon but becomes an actor in the drama of creation and history.
We attempt to realign with our Maker's will on Rosh HaShana; Hashem's Shechina descends to and visits our shuls and homes to be the vehicle of cleansing us from sin. This is followed by the overflowing joy of Sukkos in which Hashem, so to speak, invites us into His house - as the verse recited daily from the beginning Elul through Shemini Atzeres states: "for he shall hide me in His sukka on a day of evil" (Tehillim 27:5). Our relationship is hopefully restored: Hashem visits us; we visit Him. What more fitting demonstration of this mutual connection which G-d, in His infinite kindness, bestows on lowly man than the mitzvos of Sukkos which are taken from the fixed, Divinely dictated Torah shebichsav, halacha l'Moshe miSinai - the oral tradition preserved by the Jewish people, and the dersashos, which, through human analysis bridge the two. May we merit bringing the teshuva of the Yamim Noraim and the joy of the re-establishment of our partnership with our Creator to the rest of the year!
[1] Many other sources for this concept of partnership exist. See, for example, several essays in Rav C. Y. Goldwicht's Asufas Ma'arachos at length.