There is a machlokes Tanaim how to resolve the contradiction between the pesukim "atzeres l'Hashem" and "atzeres lachem" -- which one is it? R' Yehoshua holds that you have to make a compromise and split Yom Tov between G-d and your own enjoyment; R' Eliezer holds it's either/or -- you can spend the day immersed in Torah and avodas Hashem, or you can spend the day immersed in doing what you enjoy. This machlokes fits a general pattern of disputes in Chazal as to how to handle situations where there are contradictory pesukim or halachos and no "kasuv ha'shelishi" that resolves what to do: are you supposed to make some a compromise between the two extremes or choose between fulfilling one or the other. (The two pesukim in this case appear in two different contexts with respect to two different yamim tovim, but the gemara was not willing to entertain the possibility of reading each pasuk as applying only to its particular yom tov context as a feasible answer.)
Maharasha (Pesachim 68) asks: according to R' Eliezer, if one spends the entire day immersed in Torah, how can one fulfill the mitzvah of "v'samachta b'chagecha?"
He answers that learning gufa is simchas Yom Tov! What could be more enjoyable than a blatt gemara? (R' Tzadok haKohen writes that the "atezeres lachem" is fulfilled by the joy in learning; the "atzeres l'Hashem" should be how you approach eating your meal -- it should be l'shem shamayim.)
R' Zolti suggested based on this Maharasha that when one learns on Y"T, aside from the kiyum mitzvah of talmud Torah, one gets an additional kiyum of simchas Y"T. This may explain a difficult Rashi in Sukkah (25). The Mishna tells us that people who are engaged in doing a mitzvah are peturim from sukkah. Rashi gives as an example someone who is travelling to learn Torah. Achronim ask: the rule of oseik b'mitzvah patur min hamitzvah normally does not apply to talmud Torah -- we assume that you have to stop learning to do mitzvos. The raison d'etre of learning is to perform mitzvos, so it makes no sense to say that learning should supersede doing mitzvos. How then could Rashi say that someone going to learn is exempt from the mitzvah of sukkah?
Some of the Achronim answer that Rashi is not speaking about learning itself. but about travelling to learn, and the travel, the hechsher mitzvah of going to learn, is what creates the exemption (which itself is an interesting chiddush -- the hechsher mitzvah of a mitzvah which itself does not exempt one from sukkah can create an exemption). In the sefer "M'Shulchani shel R' Eliyahu Baruch" from the Mir he quotes from his son that based on R' Zolti's chiddush, Rashi makes perfect sense. When one is learning on Y"T, it is also a kiyum of simchah. It is not the mitzvah of talmud Torah which exempts one from sukkah, but rather it is the kiyum mitzvah of simchas Y"T inherent in that same act of learning which does so.
R' Eliyahu Baruch did not like this approach and argued that it's not the kiyum hagavra of learning that does not allow any an exemption from mitzvos, but rather the cheftza of Torah itself is overridden by any other mitzvah. Therefore, whether the kiyum mitzvah is one of simchas Y"T or purely one of talmud Torah does not matter in the end.