He [Rabban Gamliel] said, "Treat His will as if it were your own will, so that He will treat your will as if it were His will. Nullify your will in the face of His will so that He will nullify the will of others in the face of your will."
I do not have a part with the first problem of this statement. Much like one would not scrimp on a huge investment such as a house, one does not settle for less on one's own spiritual life (Ruach Chaim). One is to treat their relationship with G-d that is as intimate as the ideal marriage. It's like any covenantal relationship: a marriage is about harmony in the home (שלום בבית) and understanding the other partner to the point where one compromises where needed. Like any other relationship, it is a two-way street.
Once I came across the second portion that talked about nullifying one's will, that is when I found it to be very problematic. The verb בטל is used in the passage as "to nullify," in the sense of "to cease" or "to abolish." According to the Kozhnitzer Rebbe, there are times that we should pray to G-d to take away our free will. Unfortunately, there are many Orthodox Jews that feel this level of unquestioning obeisance.
I know it's easier to succumb to groupthink or conform to an establishment than it is to have an authentically independent mind, but how can a Jew think that submission is a Jewish value? The name of the Jewish people is ישראל (Israel), which literally means "[He who] struggle[s] with G-d." Asking a Jew to nullify the very thing that provides the namesake of what it means to be Jewish is asinine. Essentially, if you're not struggling with or questioning your Judaism, you're not doing it right. This is especially true when we consider that the last time G-d explicitly said anything in prophecy was well over a millennium ago. Even with that in mind, all of this assumes that the tradition has been transmitted absolutely perfectly, the rabbis have correctly understood G-d's will 100% throughout history, and also assumes that the halachic system doesn't have any glitches. I cannot make any of these assumptions without having some reservations, hesitations, or doubts on my end. As a result of the skepticism and struggling with G-d, Judaism becomes a modus operandi that allows me to ask the bigger questions of life and analyze my beliefs and practices on a regular basis and on a more profound level.
If G-d wanted to make us as angels, trust me, He could have and He would have. But G-d endowed us with free will. He endowed us with the ability to question. Think about the Passover seder: the child who cannot even ask a question is lower on the totem pole than the evil child (*gasp*). Abraham questioned G-d before He destroyed Sodom and Gommorah. Moses questioned G-d by reminding G-d about His promise to the Jewish people (Exodus 32), after which G-d subsequently "changed his mind." These are but some of the examples in which Judaism illustrates its famous reputation for permitting one to ask a good question and not live in spiritual passivity and complacency.
Pirke Avot is a text of ethical ideals, but the problem with setting such high standards is that being human means making mistakes and being unmistakably imperfect. As laudable as it might seem to eliminate all our flaws to the point of nullification, it is just not possible. It is a verse such as this one that engenders the all-or-nothing mentality that permeates throughout much of Orthodox Judaism. I am all for Jews studying Torah and performing mitzvahs as much as humanly possible, but let's do so with an appreciation and understanding of the human condition.