The revelation of the enemy is a big letdown in GFIII.
In the first 2 movies, the Don deduces who the hidden enemy is via intuition and a series of ambiguous clues that we discuss here on a daily basis.
In GFIII, it's more like:
Michael: Who's our enemy?
Tomassino: Don Lucchese
Michael: OK, let's stab him with his eyeglasses.
Not quite as deep or memorable.
Well, wasn't Mike relying on Tomassino's knowledge and intuition?

Actually its more like:
Michael - Whose our enemy?
Don Tomassino - Luchese
Micheal - I need to see a cardinal.
Cardinal - Why are you sitting down?
Michael Do you have any candy and orange j.....
Cardinal - Voila! Want to go to confession?
Michael - I killed Fredo.
Connie - Too bad Fredo Drowned.
Michael - I cant handle this anymore, Vincent, please take over.
Vincent - Ok, I'll arrange to have Calo kill Luchese with a pair of Eyeglasses.
Connie - Have a canolli.
Bang.