Rav Tzair has a an excellent series of posts that analyse the conceptual basis underlying a Midrash of the weekly Parshah. Thanks to him, I now set aside some time every week to study Midrash. The commentarues on the page are usually good for deciphering the basic meaning of the text but very rarely go beyond that.
I know Saul Lieberman has an edition of Midrash Rabbah published by Mossad R' Kook [? - or so I thought, actually by Harry Fischel] but I'ven never seen it [Found it on Otzar HaChochmo thanks to andy - introduction + notes , he is at his most useful when explaining an obscure Greek term] so I don't know what its about. There are critical editions of a few chapters of different Midrashim created as doctoral dissertation but I don't know if any of these have been published. From the traditional sphere, Midrashim are fodder for drash and so their p'shat aspect is very rarely explored. Is the notes to Kasher's Torah Sheleimah worth looking into? How about Ginzberg's Legends, there must be valuable material in the notes there?
So, has anyone got any recommendations?