I originally was unimpressed by the Ultramarines. On my first pass the only thing I really liked about them was the flexible Characteristic bonuses. Even their Chapter patterns seemed meh. And then I realized how powerful Lead by Example really is...
The key is that, if used by a Tactical Marine with Tactical Expertise, all members of the team start putting out the bonus. That means that your Kill-team can gain a bonus to all actions equal to the sum of their total Fellowship bonuses. In a five-Marine Kill-team, that can easily be +20 from the start! And then each Marine can give one re-roll per turn! After Rank 4, the bonus doubles, so it shouldn't be too hard to have very nearly +50 to everything (assuming a few members of the team have upped Fellowship)!
Smurfy!
Crazy...