Ok, I finally finished the game after 37hrs of gameplay...sort of.

I am the Don.
I have 100% of :
Missions, hits, favors, safehouses, rackets, fronts...if you look at the primary objective screen everything is 100% except the final tally of 'Game completion' which is 89%.

It is now telling me that in order to become Don of NYC I have to:
Take over all rackets/fronts ---- I have
Purchase all safehouses and all executions ---- Have all safehouses and about 45% of execution styles

I read on someone's walkthrough (I didn't use it to beat the game, just to try and answer this question) he said that he had 90% and didn't even have much of what I have listed above. In fact, only difference was that he had collected all of the mission money bags, of which I have 0. Yeah, kinda sad.

So, does anyone know what it takes to become Don of NYC? Do I really need to go through all of the execution styles? Just have 90%+ completed....any suggestions.

I didn't need all executions to get Don of NYC. Just needed to complete the missions and take over all the businesses and rackets. If you're sure you have all the properties, I really don't know what to tell you.

If it makes you feel better, the game ending cinematic is pretty boring, anyway. It's just a silent scene of you acting like an even bigger boss than when you became Don of the Corleones. :P

you have to take down all of the compounds..then you will be the don of NYC

You need a few more execution styles to get just over 90%. I've read about this problem several times before and this is what it always boiled down to.

Have you dynamited most of the safes, robbed the banks, and did all the prize fights?  I haven't taken every business or racket yet and I am the Don of NYC.  I have over 80 of the safes cracked and about 55 of the film reels (I won't bother getting them all). 

For anyone else playing this game, I highly recommend that you do ALL the executions before killing off the Tataglias. 

I had the very same situation.  Just stopped playing the game after that as I couldn't be bothered to learn all the execution styles.  Would have been nice to see the ending but I didn't think it was worth it.  I got enough satisfation taking over the whole of NYC.

There are three possibilities.

Recheck all of your fronts you may have a non gang affiliated hidden racket. Basically no gang affiliation means a racket can hide under your front, and be invisible on the map. You need to start systematically checking your fronts.

Make sure you have blown up all of Solozzos drug houses. Somehow you can go through the entire game without doing this. Since it is not a mission itself, but a general command. I think you have to do this the Godfather asked you to.

Make sure you finish every fight. Do not worry just pull out a gun and wax them if they are too hard. Call it cheap but it at the very least gets rid of those mission.

I will bet you have missed a drug house, and that is it. If not finish the fights by cheating, and if that does not do it check your fronts. That is all you should need. I assume you have knocked off all the icons. I do not think you need the executions, the money bags, or the banks. I got don without finishing the banks or grabbing all the bags. I sure as hell know you do not need the reels. Not sure if I did all the executions if I did it was purely unintentional.