So I've been looking for a book, idealy, that disects "Philosophical Investigations" remark by remark from start to finish, and just explains everything remark by remark. — Amit Mish'an

I believe what you're looking for is a series of books, the first of which is Wittgenstein : Understanding and Meaning, Volume 1 by PMS Hacker. There are also some summer courses offered by Cora Diamond and James Conant which go aphorism by aphorism within some delimited sections of the book. The audio is definitely floating around the web (pretty sure you can find the link if you check out Conant's UChicago website). Not to mention a lot of great lectures and programs you can find by typing his name into youtube or itunes podcasts (e.g. "In Our Time has a great episode on Witty).

Personally, I would recommend you consider a small book to start out with: Hans Sluga's Wittgenstein.

Like any big philosopher there is a mountain of literature on him so there's a lot more to point to. But those are definitely good starting points (along with Ray Monk's biography if you're interested in his life at all).

The answers you get from people on this forum are probably going to reflect their bias toward a particular interpretation. I would read as much background information as you could on Wittgenstein, and how he developed his ideas. If I were you I would read Ray Monk's book Ludwig Wittgenstein, The Duty of Genius, it is widely regarded as one of the best book on Wittgenstein.

First of all - thanks again, to both of you, for the recommandations.

Please take into consideration the fact that I'm not looking for a book about Wittgenstein's life or the entirety of his works, but just a "targeted assault" on the Philosophical Investigations, perhaps, ideally, as cold and clinical in nature as the Investigations themselves.
Plus, please take into consideration the assumption that I "pretty much get it" and am looking for a more exhaustive "tractatus" of this work (not a "Wittgenstein for dummies" introduction books :-D ).

Considering those factors, do you stand behind those recommendations you've made?

Neither of us recommended anything a grad student writing on Wittgenstein hasn't read. The summer school I mentioned is for professional and budding scholars focused on Wittgenstein as an AOS. Beyond that you'll have to look into the books yourself to see if they fit what you're looking for. There's not much more we can offer unless you want more targeted advice -- e.g. "Can someone give me the lay of the land on the literature surrounding McDowell, Kripke and Cavell on rule-following?" -- or more general recommendations (though that stuff should be clear enough: Cambridge Companion, Routledge Guide, etc.).

O.k, then. You've been very helpful and I will most certainly look into your recommendations.

Thanks so much!

Good luck! Feel free to PM me if you don't like the direction we pointed you in or if you need more recommendations.

That is so kind of you! Thank you :-) :-) :-)

And if not - can you recommand the closest book to the concept I'm looking for? — Amit Mish'an

The Hacker and Diamond/Conant recommendations above are good for the specific thing you asked for (Hacker's a bit out of date and a bit idiosyncratic in places, Diamond and Conant are more au courant, and really excellent IMHO), but wrt the broader question of generally getting a handle on what the later Wittgenstein was banging on about, I highly recommend the book of lecture notes by Alice Ambrose, a Cambridge student of his: Wittgenstein's Lectures: Cambridge, 1932-1935

It's not specifically a book on the PI, and the lectures are from a time before he wrote the PI, it's also not a book it would be wise to take seriously as a detailed guide to W's thought (after all, it's just notes, and as a young student she may have misunderstood some things), but there are some neat formulations you don't find anywhere else that I think give a good entry point or inroad into a better understanding, and it's a very alive-feeling book, that gives a good sense of Wittgenstein thinking on the hoof, and of his excitement as a philosopher in the process of discovery. At any rate, it's what "unlocked" the PI for me.

Thank you, gurugeorge! I will most certainly be looking into that.

It's a great recommendation! Do you know of anyone good, other than Baker & Hacker, who fit the OP's criteria of writing a commentary that takes on the PI aphorism by aphorism?

I recommended Hacker/Conant/Diamond because those are the only high-quality examples I'm familiar with and in many ways they are among the few excellent philosophers who don't attempt to subsume Wittgenstein's thought into some broader historical interest or wider project. (When OP says he wants somebody "cold and clinical"... you think Hacker, no?) I much prefer C&D, but I think Hacker works as a great foil for them.

Do you know of anyone good, other than Baker & Hacker, who fit the OP's criteria of writing a commentary that takes on the PI aphorism by aphorism? — John Doe

No, as an amateur of philosophy that's as far as my knowledge of detailed commentaries on the PI goes too! :) Although there are umpteen "introductions" to W. (Stern, Grayling, etc.) I really don't think there are any others with that kind of fine-grained approach. (Maybe Kripke, who wrote some detailed stuff on a few passages, IIRC? I haven't read those, but they're probably worth checking out.)