I find initiative very confusing in ArM5. In theory you only roll it once. But in many circumstances a given individual has several initiative bonuses. For example, a magical beast might have different initiative bonuses for its bite, its claw, and each of its powers. How do you all handle that? Retain the first initiative total? This seems to be the rule. But then many would use a high initiative thing first to basically get a free action over what they would have had if they started with the low initiative thing they're going to switch to. Retain the first initiative roll but adjust the total? Reroll initiative each round? These two seem to function better except that they add a lot to the die rolling and thus cut down on the fluidity.
My belief is that "retain the first initiative roll but adjust the total" is the RAW.
A little off-topic: I think of initiative as just a mechanical gambit to set the order of play, not something intrinsic to the combatants. That's why the original fast-casting rules always bugged me: someone gets a lucky initiative roll to start the battle, so they're essentially immune to being fast-casted on throughout? The optional fast-casting rules in Lords of Men are a big improvement to me.
Certainly the more rolls there are the more significant your initiative modifier is likely to be.
I know it was slow and fiddly in play but I must confess a conceptual soft spot for the 4th ed combat system with 3 melee ranges and initiative letting you control the distance. Yes I did play a Quickness 5 longsword and dagger fighter