The problems I see are:
Aztec
Berbers
Burmese
Burgundians
Celts
Chinese
Ethiopians
Huns
Franks
Incas
Indians
Italians
Khmer
Malay
Malians
Mongols
Portugeuse
Saracens
Sicilians
Slavs
Spanish
Vietnamese
- some civs are consistently strong (across many maps and modes (dark age start and feudal age start)), e.g. Franks, Chinese
- some units / techs are somewhat useless or overpriced or underpowered relative to generic units, e.g. Genitours, Missionaries, Stronghold (Celts CA UT), Madrasah (Saracens CA UT)
- some civs need a boost, e.g. Italians and Portuguese (on land maps, but not water maps), Spanish (but not for Castle rush into conqs)
- Elite Steppe Lancer: armour from 0/1 to 0/2
- Fishing Ship: can drop off food at Town Centres (useful on Mangrove/Swamp terrain)
- Transport Ship: training time from 46 to 50/45/40/35
- Fast Fire Ship: +3 vs Buildings reduced to +1
- Fast Fire Ship: gains +2 vs Standard Buildings (if Masonry is researched then this basically increases their damage vs buildings from 1 to 2)
Aztec
- Jaguar Warrior: HP from 50 to 55
- Elite Jaguar Warrior: upgrade cost from 1000f,500g to 800f,800w
Berbers
- Genitour: bonus damage vs cavalry archers from 0 to 1
- (Elite) Genitour: food cost from 50 to 45
Burmese
- Cavalry +2 bonus damage vs standard buildings
- Relic vision bonus changed from team bonus to civ bonus (the player can still ping the location of the relics; allies can see the relics with a market)
- Team bonus: Monasteries can garrison nearby relics without a Monk (within 4 range)
- (Elite) Arambai: +1 damage vs standard buildings (not affected by civ bonus vs standard buildings)
- Manipur Cavalry: moved from Imperial Age tech to Castle Age tech
- Manipur Cavalry: cost from 650f,400g to 300f,300g
- Manipur Cavalry: bonus vs standard buildings from +6 to +4
- Howdah: moved from Castle Age tech to Imperial Age tech
Burgundians
- Elite Coustillier: upgrade cost from 1000f,800g to 800f,800w
- Flemish Revolution: only converts male villagers to Flemish Militia (i.e. female villagers (~50% of villagers) remain villagers)
Celts
- Siege weapons fire 15%/25% faster in Castle/Imperial Age (down from 25% in all ages)
- Stronghold: affects all buildings (i.e. TCs in additional to Castles and Towers)
- Stronghold: grants buildings +2 damage vs Standard Buildings (affects primary AND secondary arrows)
Chinese
- (Elite) Chu Ko Nu: training time from 16(13) to 17(14)
- Elite Chu Ko Nu: upgrade cost from 950f,950g to 1000f,1000g
- Great Wall: cost from 400w,200s to 400w,200f
- Rocketry: cost from 750w,750g to 800w,800g
Ethiopians
- Elite Shotel Warrior: upgrade cost from 1200f,550g to 1000f,700w
- Royal Heirs: cost from 300f,300g to 250f,250g
Huns
- (Elite) Tarkan: Attack rate from 2.1 to 1.9
- Atheism: cost from 500f,500g to 500f,500w
Franks
- Mounted units HP bonus from +20% to +10%/+15%/+20% starting in the Feudal Age
Incas
- Team bonus: Houses and Farms build 33% faster.
- Andean Sling: additionally grants 20% faster projectile speed
- Elite Kamayuk: upgrade cost from 900f,500g to 700f,700w
Indians
- Elite Elephant Archer: upgrade cost from 1000f,800g to 900f,900w
- Shatagni: Hand Cannon range from +1 to +2
Italians
- Gains access to unique armour upgrades at the blacksmith which affect infantry, archer, and cavalry units at the same time (Simply: there is one armour upgrade per age for all unit types (infantry, archers, and cavalry)). Loses access to the regular Archer Armour, Infantry Armour, and Cavalry Armour upgrade lines. Details for unique armour upgrades: Armour 1 (+1/+1; 150f); Armour 2 (+1/+1; 200f 150g); Armour 3 (+1/+2; 300f 250g).
- Silk Roads: additionally reveals the 4 corners of the map (20 tile AOE from the corner; i.e. the fog is revealed, but you don't have permanent vision)
Khmer
- Villagers garrisoned in Houses regenerate at 6HP/minute (same as Towers and TCs; up from 0HP/minute)
Malay
- Each initial military production building costs 50% less wood (i.e. the first Barracks costs -50% wood (and the next one costs the normal price), first stable costs -50% wood etc.)
Malians
- Tigui: additionally grants TCs +1 pierce damage
Mongols
- Nomads: gold cost removed
- Nomads: affects all forms of population (not just houses; i.e. you won't lose population when you lose a Castle or a TC (or a military building, given a Slav ally))
Portugeuse
- Start game with 20 tile AOE around TC explored but not visible (i.e. the fog is revealed, but you don't have vision)
Saracens
- Madrasah: changed to "Monks +2 conversion range, healing range, and LoS"; cost increased to 200f,450g
Sicilians
- Heated Shot and Arrowslits are free
- Donjon: damage vs Ships and Fishing Ships increased from 7 to 9 in Castle age and 7 to 10 in Imperial Age (matches Guard Tower / Keep)
Slavs
- Infantry units +2 LoS
- Orthodoxy: additionally grants +3 armour vs anti-Monk attacks
- Druzhina: food cost reduced from 1200 to 1000
Spanish
- Castle Age unit line upgrades don't cost gold (Elite Skirmisher; Pikeman; Light Cavalry; Long Swordsman; War Galley)
- Missionary: can dismount to pick up relics. Moves at the same speed as a Monk in dismounted form. Reverts to mounted form upon dropping the relic.
- Missionary: healing per minute increased from 150 to 200
- Conquistador: training time increased from 24 to 25 seconds
- Elite Conquistador: training time decreased from 24 to 23 seconds
- Elite Conquistador: attack delay decreased from 0.42 seconds to 0.2 seconds
Vietnamese
- Battle elephants +20 HP
- Chatras: from +100 HP to +80 HP
- Paper money: additionally grants the player (but not the allies) a trickle of gold (equal to that of 1 relic)