Hirhurim posts a mini-review of the translation of A Y Heschel's Torah Min HaShamayim. (I highly suggest that anyone who can seek out the Hebrew original as the beauty of Heschel's Melitzah, as well as many of the notes, is lost in the translation.)
Here is Lieberman's opinion of the book(s).
I agree with Hirhurim that Heschel doesn't seem to have made any especial effort to connect the transmittor of the pericope with a specific shool. Eg. He will quote a "rationalist" statement of R' Huna and then place it within the school of R' Yishmael without showing how R' Huna would e connected with the disciples of R' Yishmael.
A more significant criticism can be found in Menachem Kahana's entry on Midrashei Halachot in NEJ. Here is a relevant quote:
"R. Ishmael and R. Akiva also differ regarding the permissibility of expounding certain topics in public. R. Ba, in the name of Rav Yehuda (TJ Hagigah 2:1, 77a), attributes the law in M. Hagigah 2:1: "The forbidden sexual relationships may not be expounded before three persons" solely to R. Akiva, and as opposed to the opinion of R. Ishmael. Sifra (from the school of R. Akiva) accordingly did not include expositions regarding the forbidden sexual relationships in the portions of Aḥarei Mot (Lev. 18:7–23) and Kedoshim (Lev. 20:10–21), while the second midrash on Leviticus (from the school of R. Ishmael) does contain in these portions expositions of this subject, some of which were artificially included in several manuscripts of Sifra. Several explanations were offered for the reason behind this disagreement. I maintain that R. Akiva's position is to be understood in light of his extreme exegesis and his fear that the publicizing of such expositions on the subject of forbidden sexual relationships, that human nature craves, was liable to result in licentious behavior "and may come to permit that which is prohibited," in the words of TB (Hagigah 11b) on this mishnah. In contrast, R. Ishmael, who adopted a more moderate exegetical method, did not fear publicly expounding the passage of forbidden sexual relationships, presenting its prohibitions and concessions based on his hermeneutical rules. The halakhah in M. Hagigah loc. cit that "the Story of Creation is not expounded before two" is similarly attributed by R. Ba in the name of Rav Yehuda in TJ idem as following the view of R. Akiva exclusively, in opposition to the opinion of R. Ishmael. This dispute is reflected in the disagreement between the two tannaim concerning the legitimacy of the exposition in Gen. R., p. 12, of the word "et" in Gen. 1:1. R. Akiva explains his position that the word is intended to prevent an erroneous Gnostic interpretation, that "we would say that the heaven and earth also are divinities," and therefore nothing can be derived from it, while R. Ishmael has no qualms in expounding the word et in this problematic verse of the act of Creation. Gen. R. p. 206 and p. 574 also contains a similar disagreement between these tannaim concerning the exposition of the word "et" in two other verses that are likely to be understood as supporting the view of the heretics; here as well, the dispute between R. Akiva and R. Ishmael is based in the different nature of the hermeneutical method of each Tanna. R. Ishmael was not wary of expounding these verses, while R. Akiva was apprehensive that the public exegesis of such sensitive verses in accordance with his extreme expositional method would be liable to serve as justification for the extreme interpretations of the heretics, following their methodology, and he therefore refrained from expounding them in public.
In light of the above, we cannot accept the opinion of Heschel that R. Ishmael was a rationalist who vigorously opposed esoteric expositions of the Torah and matters that cannot be attained by the intellect. More generally, the drawing of unnecessary connections between simple and literal interpretation and religious rationalism should be avoided."