Does the entire Haggadah have to be read word for word, or it is enough to just ‘talk’ ABOUT some sections without actually reading the text?
Torah law requires every Jew to discuss Yetziat Mitzrayim on Seder night.
Sefer Emek Brachah famously quotes Rav Chaim Soloveitchik as pointing out that there are three particular parts to the mitzvah of Haggadah: the question and answer format of the Haggadah (Mah Nishtanah… Avadim Yayinu…), the requirement to be Maschil bignus umesayem bishvach (to begin with the “low” part of Klal Yisroel’s history and end off with their “highpoint”), and the requirement stated by Rabban Gamliel to discuss the three mitzvos of Pesach, matzah and marror. This is interpreted by some to mean that these three aspects of the Haggadah are midoraysa – mandated by Torah Law.
Other parts, such as the requirement to read the Pesukim from Arami oved avi and onwards, and to read the explanations expounded by the Sages, are Mishnaic (if not earlier) in origin, and are mandated by Rabbinic law. So is the requirement to say Hallel (the requirement to say Hallel is actually alluded to in the Prophets (Yeshayahu 30:29)).
The standard text of the Haggadah has been universally adopted by all Klal Yisroel for possibly two millenia, and where possible all of it should be recited or at least listened to. (And of course, as the Haggadah itself says, whoever expands on the subject is praiseworthy!) In addition it is important that one understands what is being said, and if not it should be translated into a language that those present will comprehend.
See Shulchan Aruch, Orach Chaim 473:6, and Mishnah Berurah note 64.