Fulgrim. Called the Phoenician. Sire of the Emperor's Children. Possessed of Chaos and subsequently freely devoted to Slaanesh and elevated to a daemon prince. But in the early days of the Great Crusade, still a sane and devoted general for humanity who was simply prideful and sought to be the best he could at all things, including warfare. That much and more can readily be said about this primarch. But do his rules back up his … style?
The first thing to note is that Fulgrim is one of the cheapest primarchs available and he is therefore readily in the category of "probably should take him if I can have a Lords of War" for the Emperor's Children.
His seeking for perfecting in all theatres of war is reflected in his Strategic Planning special rule which is a solid way in which his army can tailor itself to new opponents without having to re-write the army list. Also, it is reflected in his Sublime Swordsmanship skill -- the ability to have a 3++ save only in combat means the player should (must!) seek out close combat as soon as possible for him.
But unlike his brother, Angron, Fulgrim is more than a simple melee expert. He grants an amazing +2 combat resolution to himself and his sons. Why is this amazing? Well, 30k space marines do not have "And they shall know no fear", and hence can very much be swept away. This rule alone will almost dictate the play style for the Emperor's Children: get in combat early, strike hard at high initiative (higher than the enemy at any rate!), win the combat and sweep the opponent away in one combat round (preferably). Clearly in some cases, this requires many bodies, but in others, an elite cadre with high initiative and plentiful power weapons (or similar) can get the job done.
And there's more! He has an Alpha Legion like ability to bring on his reserves: all reserve rolls can be re-rolled as desired. Hence an all deep striking army will be hard to counter and has the real possibility of alpha striking an opponent off the board before the game terminates. But its all about getting those bodies on to the board and in to the correct positions to pull off the kind of game that the Emperor's Children want to.
Fulgrim's weapons are nothing too special: an AP2 sword, 2+/5++ and a volkite. Get him in to combat where he needs to be, frankly.
Overall, a cheap primarch and one that is tailor made to a particular play style. Play to his strengths!