Good, but I don't want experience to replace actual items or prizes we would normally get. There should also be a limit to how many skill points you could get, such as in Borderlands 2 or Darksiders II, or else people could grind and become ridiculously powerful. There should also be multiple trees, each suited to a different style of gameplay, or to different abilities.
Well, I wasn't exactly planning for people to become extremely powerful really fast. More like there would be a progression in the level of difficulty as the adventure went on; enemies would start out easy or be fairly effortless to defeat, and rightfully increase in difficulty (from easy to medium to hard) before the game's end. This would allow the player to accumulate experience points accordingly, and be an optional system for casual players, again like me, as it would effectively make the game easier. Honing certain skills [or not] would give them an equal chance to overcome harder foes; or a hardcore player could omit the skill tree and play to their heart's content.
And actually, I did specify that experience could be used to upgrade weapons and more, not replace them:
So...I'm thinking that a "skill tree" supplies itself with the experience that the player garners on their adventure. In order to be able accumulate these points, they must kill certain foes (the harder they are, the more they get) or complete objectives that NPCs distribute. Once this is done, they'll have the ability to scour through a menu of "branches" [or in other words, catagories] and deduct points as they see fit. The skill tree can be used to upgrade weapons, attacks, magic, defense/offense variations, and individual pieces of armor, which I've been wanting to see added for a long time now.
The killing enemies to get exp... I don't want to have to grind in Zelda.
Now a better way to fit the style of the game with out changing it, is say when ever you complete a piece of heart or get a heart container, you also get a skill point to spend or something like that?
As I laid out above, the "grinding" would be optional; but without it, the going would get harder.
Aside from that, your latterly suggestion is good, except for the fact that, knowing Nintendo, we'd probably receive a secondary text menu telling us that we got one skill point, in additional to the heart piece/container tally. It'd be pretty repetitious to me (just how I am). Not to overrule you in any way, it might be better to gather experience just by completing missions, and do away with enemy killing for exp. You'll recall that Skyward Sword had an entire series of sidequests that we got Gratitude Crystals from. Well, this system could be likened to that, except...with experience points.