The key to keeping a game non-linear in terms of player build are twofold, having different skilltrees and having the ability to allocate stats. Im going to focus a discussion on stats and take in some input.

--Disclaimer--
This is going to be focusing on Naruto GOA, if you dont want to talk about Naruto GOA then stop reading now and get the Fawk off my Member page.
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The 3 statbar stats, that is stats that get depleted and serve as an HP/MP for the game are:
Stamina: Similar to HP, this stat regenerates and is more a guage of how much physical energy your character has, on top of being the stat thats depleted from most attacks, this stat will also be used up to use certain skills (taijutsu)

Chakra: Basically MP, this is expensed and regenerated and is used by most ninja skills.

Wound: When you take damage from piercing weapons, assassination techniques or run out of stamina you gain wound, wound is only healed when you seek medical help or a bed. Getting 100% wound typically means a death.

The above arent really the topic of conversation as i dont really think they need changing, however they impact the following vital attributes that make up a character build:

Str: Strength, effects max stamina, stamina regeneration and melee(taijutsu) damage.

Rfx: Reflex, effects how often you land hits, how often you avoid hits and also the ability to land Wound damage hits from swords/knives and assassination techniques (conversely the ability to defend against these techniques).

Con: Control, effects maximum Chakra, Chakra regeneration as well as the effectiveness of many skills such as Medic (both medic ninja offense techniques and healing technique effectiveness).

Int: Intelligence, effects how many skillpoints you gain per level (Skillpoints are spent on skills and passives). This effect is cummulative, meaning that players who invest in int early will end up with more skillpoints later because you gain skillpoints Dependant on both how many skillpoints you have in total at levelup AS WELL AS how many skillpoints you buy that level (significant bonus). Int also effects Genjutsu, aka illusionary techniques in terms of defence against and offense with. Genjutsu tends to avoid combat more than anything, binding and putting opponents to sleep.

The current issue with GOA is that many skills do static damage, these skills tend to have other effects that make it so they never become obsolete, however theres an issue with Con being an immensely under appreciated vital attribute. It seems once people get to a certain level they are happy with the amount of chakra they have. Now this is not always the case because some techniques have a scale Dependant on how much chakra you have in total, however theres still a need to make this vital point more relevant to all characters.

My options:
-Make CON a part of a variable aspect of damage from skills that are currently static damage. (ie fire would be 1000 stamina damage + 5*CON) (CON would range from between 50-350)

This option is something im seriously considering, It effecting damage for fire,water,earth,wind primarily as well as one of the raiton skills.

-Cut Chakra Regeneration: Basically if i was to make chakra regenerate much slower then the idea is nomatter what build you have you would want more chakra and as high a regen rate as possible.

-Change the costs of skills severely, making low level skills have the same cost but making it so that high scale and power skills would require very high amounts of chakra per use. This would make it so in order to afford to use even once a high level skill, a player would need fairly high CON.

-Keep it the same :S

Any suggestions? at current ill probably do the first option of implementing a variable component to now static technique damages from CON.