Maybe even make the skills cost more, after 1 or 2 levels I can pick all 4 every time, I think it would be better to force more specialization.
It already does that tho. Blood buys level-specific upgrades, but the amount of blood you have when you die counts as EXP to your general level. The general level lets you unlock new locations and every level gives a point to spend on a permanent upgrade across the game.
You CAN buy everything, but the more you spend the less your time is worth at the end of the day.
Besides that, leveling up in-game gets exponentially harder, so if you throw away abilities you bought upgrades to, the less damage you will do, which will make you take even more time to have the opportunity to buy a upgrade that is relevant to the new ability, so there's a point in-game where it is not long worth it (timewise) to change your build, at least for Midgard, the current available level.
I'd like to see more reasons to use the normal melee attack, as you can make a ranged build and just forget about it so far
I commented a build that really rewards you for being offensive, but not totally melee, tho. Check it out.