I know there are few build-up series (Day of Vengence, Villians United, OMAC Project etc..) to Infinite Crisis. Any of them is really necessary ?
I've read the first pages of it in Amazon's preview ( http://www.amazon.com/gp/product/1401210600?redirect=true&ref_=s9_simh_gw_p14_d0_i2 ), and I don't know wtf is going on there. I'm supposed to feel that way ?

BTW, I'm planing to read Identity Crisis as well before it.

Understanding Wonder Woman and OMAC in advance would probably make it better to ease into (I had to Wikipedia that stuff - there's some intro but still jarring without backstory). I read Infinite Crisis without any precursors and was able to enjoy it but needed to do some research first. I'm not sure specifically which lead-in books are more relevent. When I read IC it was as more of an introduction to DC Comics and I'm still a relative newbie...

Certainly Crisis on Infinite Earths is mandatory, I assume you've covered that.

The buid-up series are not really necessary.

But you should have a good general knowledge of the DC Universe (including old stuff like Crisis on Infinite Earths) and it's characters.

Yep, I've read COIE.

But it seems like IC is really throwing the reader into the deep water. WW has killed a man ? The trinity are pissed at each other ? Demons at LA ?

I agree that going into Infinite Crisis blind without reading recent precusors is really confusing since it's so different from the status quo.

The OMAC Project is pretty much necessary. And it's a very good comic too. It will explain what's up with Wonder Woman and Brother Eye. I think Identity Crisis is also something you should read, to know why Batman would build Brother Eye, and that's pretty much where the problems between heroes started, why no one really likes or trusts anyone at the star here. And it really is a brilliant, phenomenally well written comic.

Villains United is maybe not absolutely necessary, but it's another good one, and it will clear some things up. Day of Vengeance you can do without, though I liked it too.

You should read Identity Crisis (which is really a great story), The OMAC Project and the Sacrifice storyline (Superman #219, Action Comics #829, Adventures of Superman #642 and Wonder Woman #219).

That should explain more or less everything.

I see it as a reboot event like Flashpoint.
Although reading Previous story arc is not necessary but you will have to know connection between characters (that you can do by reading character bios on wiki).

I think that's a really bad analogy. Flashpoint stands entirely on it's own, and reboots almost anything. Infinite Crisis is the climax of a few years of build up, stands on the foundation of decades of stories, and while it did shake up the status quo, it still left us with the same heroes and their stories going foreward.

Tell you what, my plan is to read Final Crisis.

To do so I want to read as much as I can to understand it better. The plan is Identity Crisis-> Infinite Crisis (with minimum Countdown material before it as possible)-> Seven Soldiers Of Victory (seems like the first volume [out of 2] is OOP in most stores... bummer) and then read FC. After that, The Multiversity.

Having said that, I still want to enjoy each and every one of the above, not just mark an X in my "to do list".

As far as I know most of the negative opinions about it (if you put aside the fact that every Morrison story is a game of love/hate Russian roullete and a tormenting challenge to keep your sanity intact) are because Superman Beyond was not part of the main series. Or something like this.

Let's go a bit more OT here: The reviews of Infinite Crisis are pretty 50-50 as well, you know why ? I think a lot of people were pissed about the whole build up thing that made them buy a lot of issues and that the pay off was not good enough, right ?

While I love most of Grant Morrison's works for Vertigo and other small publishing houses, I absolutely hate most of his superhero books.
I always thought that he was incredible proud that he knew some obscure side characters and storylines from fourty years ago and was able to transport them into today's comics (no matter if it made sense or not).
The whole writing felt completely narcissistic. Like a guy masturbating in front of a mirror, that gives himself a pat on the back afterwards and tells himself how great he was.

And Final Crisis was among the worst comic books he wrote

Honestly I'm not sure. I remember the reception of Infinite Crisis being good, but maybe I didn't follow the "media coverage" so to speak as much back then. SPOILER FOLLOWS The only common complaints I came across was that it reintroduces the Multiverse, so some people were pissed of that it ruins what the original Crisis did, and that the "original" Superman gets killed.

Personally I think that the period leading up to Infinite Crisis (starting more or less with Identity Crisis) and shortly after (until the build up to Final started) was one of the strongest periods in DC history. The build up series to Infinite Crisis were mostly very strong, Batman, Green Arrow, Superman, Green Lantern were all doing very well in their respective titles (and we had Gotham Central!), the Infinite Crisis itself was very good event and delivered good character moments with epic action, and following that we got great series like Justice Society of America, Checkmate, Secret Six, we got Sinestro Corps War in Green Lantern. Good times, good times.

Now I have the mental image of King Mob wanking over himself in front of the Moonchild's mirror from The Invisibles (while focusing on a sigil, of course).

Thank you.