Let's talk subweapon design

Today it hit me that there's one major factor of any Castlevania game that often gets sidelined during discussions, and that is subweapon design. To recap, subweapons are, as the name implies, secondary weapons often deployed by the press of the attack button with a directional key. They have existed since the very beginning of the Castlevania franchise, and have taken many forms, from glyphs assigned to arms to spells cast by charging. Needless to say, they are fairly important to the overall flow and pacing of the gameplay, even though they are technically "optional".

What is remarkable is how some subweapons of yore have managed to stand the test of time, and are fondly remembered to this day. Obvious examples of such are subweapons based on the classics, like the cross, the holy water, and even the axe. They are so good that even recent games have oftentimes good powers built around them.

However, I must note that the subweapons in recent games definitely feel like they lack something. This is especially the case for games with the soul system or such, where there are plenty of subweapons but few are anything interesting. While there are admittedly some interesting approaches taken with subweapon design, like the Killer Doll soul from Aria or Ice Needles from Portrait, they tend to get buried under many unremarkable subweapons. The most telling point is that even the subweapons that people actually remember from these games aren't because they are well designed, more because they are overpowered: Red Minotaur from Aria, anyone? 

So, what truly makes a subweapon good? As in, not the most efficient or most damaging, which are fairly easy variables to manage by a game designer, but how to make them memorable, unique, enjoyable in their feel, and more. The classic games definitely had a knack for that to a certain degree, but there's only so much you can draw from them when you have to make tons of subweapons, so I would be curious to hear your views on it.