What were Yisrael referring to when they said "ve'At Tedaber Eileinu ... "?
Ramban and Rashbam (in Shmos 20:15): They said it in connection with the rest of the Torah, 1 which they thought Hashem would convey to them directly (just as He had conveyed to them the Aseres ha'Dibros). 2
Ba'al ha'Turim: Refer to 5:24:2:3.
Ramban: Though in fact, Hashem had only planned to convey to them the Aseres ha'Dibros and no more.
Why did Moshe use the feminine term ("ve'At Tedaber Eileinu") with regard to himself?
Rashi and Ramban (citing Divrei Agadah): Moshe was complaining that they made him feel weak like a woman by preferring to hear the Torah from him rather than directly from Hashem. 1
Seforno: Yisrael were conceding that to hear the Torah from Moshe was not the same as hearing it from Hashem directly. 2
Rashi: Indicating that they did not want to come close to Hakadosh-Baruch-Hu out of love. Ramban: Hashem informed him however, that their actions were based on Yir'as Hashem, and were praiseworthy, as the Pasuk goes on to explain. See Ramban in Shmos 20:16.
Like woman whose creation was secondary to that of man.
See Ba'al ha'Turim, DH "ve'At" (#2).
Ba'al ha'Turim: Like the voice of a woman compared to that of a man.