I was playing when Signature Heroes were released and I didn't see Jagex use their character in any surprising way that differentiated them from other Quest-specific characters like Zanik or (as he was released) Arrav. It would be interesting if the game were more open ended and you could have Signature heroes as NPC companions, or if they have semi-repeatable content where you help them on an adventurer. They are rather isolated both from your overarching story, and from each other. The only memorable interaction that I had with a Signature Hero was when Raptor just happened to also be finding the cause of people falling into comas in Rimmington.
Their character portrayals aren't that great, but its not like they're offensively bad. There's basically too many signature heroes imho. It would be cool if you have a rival adventurer that's like Blue from the first generation Pokemon games. So when you start quests, sometimes he's already there talking to the quest giver. Or sometimes you get to the final boss room and found out that your rival already killed the boss and vice versa. There are times where you join in on his quest and there are times where he's your sidekick. We don't have those interactions with the signature heroes that currently exist. That's why they feel similar to bit players in other quest lines.
