In vanilla Skyrim, the only real difference between an Orc and a Breton is that one needs an additional piece of magic resist gear.
To make race choice matter, I redesigned all racial abilities from scratch. No copy-pasta from Morrowind/Oblivion - all new, fresh and still lore friendly.
Also, I modified race heights - this time, I did use Morrowind's values. And all loading screens and race descriptions were adjusted to mirror the changes,
Redguards- Removed "Resist Poison"
- Removed "Adrenaline Rush"
- Added "Desert Training"
- Added "Sandstorm Charge"
Being the most talented warriors in all of Tamriel, "Desert Training" gives them a headstart in melee combat, increasing stamina by 50. "Sandstorm Charge" is great to get ahead of any enemy during combat, since it boosts movement speed and slows time for a short duration and is usable every 3 minutes.
Nords- Removed "War Cry"
- Added "Warrior Heart"
- Added "Last Stand"
Nords are fierce warriors, and I think the new ability suits someone who fight until the bitter end. Your damage output increases as your health decreases. The boost is non-linear, and grows fast when close to death.
Imperials- Removed "Imperial Luck"
- Removed "Voice of the Emperor"
- Added "Imperial Charisma"
- Added "Tactician"
- Added "Attack Order"
- Added "Guard Order"
They used to be crappy ability-wise. Now they fill a niche by having the strongest followers, since "Attack Order" and "Guard Order" allow you to adjust your followers' speed, attack damage and incoming damage, depending on what's necessary at the moment (offense or defense). Both are lesser powers that can be used every ten minutes and last for five minutes. "Imperial Charisma" modifies buying and selling prices, and "Tactician" damages an attacker's stamina by 10% if the attack was blocked.
Argonians- Added "Protective Scales"
- Added "Claws"
- Heaviliy modified "Histskin"
"Protective Scales" reduces damage from all blade-based weapons by 25%, fitting a scaled lizard. The new Histskin works entirely different than the old one; basically, you can switch between "disabled" (everything as usual), "Health","Magicka" and "Stamina" mode. The latter three double the regeneration of their respective value, but negate the other two. Sounds like a bad deal? I bet there are a few uses you can think of.
Each mode is a power of its own, so you can easily swap using hotkeys. Also added "Claws", which is the same ability as Khajiit have (that means the bonus scales with stamina).
Wood Elves- Removed "Resist Disease and Poison"
- Removed "Command Animal"
- Added "Wild Hunt"
- Added "Wild Companion"
- Added "Wood Lore"
"Wild Hunt" increases bow damage against all non-playable races by 25%. "Wild Companion" can be used every 10 minutes and calls a leveled animal companion. The summoned companion is leveled, behaves like a summoned creature (but doesn't count towards summon limit), and varies depending on the location you are in.
"Wood Lore" allows you to enhance all arrows with a magical infusion at a forge. Infused arrows explode on impact, paralyzing all targets for one second, and reduce their one-handed and two-handed damage by 30% for ten seconds. Crafting these arrows requires 15 arrows, two empty petty soul gems and three spider eggs (creates bundles of 5).
High Elves- Removed "Regenerate Magicka" higher power
- Added lesser power "Channel Magicka"
"Channel Magicka" allows you to enhance both your spell magnitude and cost proportional with your remaining Magicka percentage. Burn your Magicka fast for better spells, switch tactically between "Channel" "non-Channel" mode, depending on enemies. Suits the image of Tamriel's most talented mages. Note that switching requires any weapons/spells to be sheathed.
Dark Elves- Heavily modified "Ancestor's Wrath"
- Added "Ancestor's Fury"
ON ENEMIES, Ancestor's Wrath now triggers automatically, once they get hit and drop below 50% health, and is not limited to one use per day. In addition to the flame cloak spell, it also adds 50% additional strength to fire-based spells. The flame cloak effect starts at a damage of 5 per second, but grows by 3 every 10 levels, up to a maximum of 17 (before bonuses are calculated in, including it's own).
ON THE PLAYER, it also carries the fire bonus, but no cloak is cast; instead, you'll get a 15% chance to avoid incoming physical damage. Players also get "Ancestor's Fury": Once per day, if your health drops below 30%, you trigger a huge explosion and two angry Dunmer ancestors arrive to aid you. They are leveled and use strong weaponry.
Bretons- Removed "Dragonhide"
- Nerfed "Resist Magic" passive
- Added spell "Twin Blood Summoning"
- Added spell "Twin Blood Eruption"
This is a very interesting one. Both new abilities are spells, not powers, and require you to sleep between uses. Both spells take long to cast and reduce health continuously while active (no Magicka cost), and also negate your passive magic resistance for two minutes. Why bother casting? Well, they have supreme effects once pulled off. "Twin Blood Summoning" allows you to summon an unlimited number of creatures while active, and "Twin Blood Eruption" doubles spell magnitude of all spells, while halving casting cost. High risk, high gain.
Orcs- Added "Orcish Smiting Lore" (25% improved tempering)
- Modified "Berserker Rage"
"Berserker Rage" is a good power, strong and with RP-value, so it stays with slight adjustments. Instead of being limited to one use per day, it can now be used multiple times, but it is required to sleep between uses. While active, you still deal double damage, and all incoming damage is reduced by 25% now (includes magic). However, the activation costs health, and while raging, benevolent potions are 75% less effective, so use some tactic. I also wanted to give them an additional passive buff though, and "Orcish Smithing Lore" seems perfect.
Khajiit- Added "Feline Athletics"
- Added "Survival Instinct"
- Tweaked "Claws"
- Tweaked "Night Eye" to be permanent/toggleable
I want Khajiit to feel like agile cats, and increasing movement speed and jump height, while reducing falling damage via "Feline Athletics" (+ 20% speed, half falling damage) seems like a logical step to this goal. "Survival Instinct" triggers once per day, if your health drops below 25%, and increases attack speed, and movement speed even further. The bonus on "Claws" is now stamina dependent; the formula is x += (0.1*stamina).