(Continued)
Slinger Inca
A more fragile Archer with a chance to withdraw from a melee attack. As many have noted, this is a very mixed ability, as this makes these units useless for protecting your civilian units. As archers are often stationed on tiles with workers to deter nearby barbarians, this has the potential to seriously harm early play. One might prefer to fix this by having the civilian always move with the Slinger, but this could seriously delay construction of tile improvements.
If a barbarian pushes your Slinger + Worker back over a river, and is killed immediately next turn, the worker has lost two turns of construction before it is back where it started. One would prefer the slinger simply take the modest hit and allow work to continue. A better solution would be to simply give the Slinger normal defensive strength and a chance to negate all melee damage, symbolizing their ability to dodge the enemy, while having them hold their ground. This would make for an all-around solid early game defensive unit.
Kris Swordsman Indonesia
A familiar and divisive unit, which gets random bonuses or penalties after first combat. This unit fails to reliably do the one thing melee units must do well, which is hold the line. The bonuses can be strong, but only help when attacking, which Swordsmen shouldn't spend much time doing anyway. The penalties, however, have the potential to be devastating to the integrity of your front line, which is completely unacceptable. Because it's random, you don't know which part of your battle line will be weakened until it's too late. This adds up to being a terrible unit, which is sad considering that the unit it replaces doesn't see much use anyway.
Making this unit worth building in the first place requires removing the Iron requirement, or else players will wait for Pikemen as they usually do. The random element can be fun, but the promotions should only be positive, or else the unit can't be trusted to do it's job at all. Promotions like the aforementioned chance to ignore melee damage, or get Cover I, or similar would be exciting to discover, and if nothing else, you have a solid front-line unit that everybody else needs to improve Iron to build.
Samurai Japan
It's a stronger Longswordsman with Shock I and Great Generals II. Alright, but players tend to skip building Longswordsman and hold on to Pikemen. To incentivize their use, it should have a higher general combat strength as well. Samurai should just feel stronger, and dominate their era a bit more than they do.
The Samurai also has the ability to construct fishing boats, to aid with Japan's UA. This is almost never used, however, since Steel is one of the last techs players will get in the Medieval Era, and by that time, they've certainly built all they fishing boats they need for the early food and luxury resources, and new cities are very rare at this stage in the game. This leaves Japan without any practical way to leverage it's UA.
The solution to this dilemma, as has been suggested by others, is to move the "construct fishing boats" special ability to the Warrior, who will also start with the ability to embark within friendly waters before Sailing. This gives Japan a faster coastal start to suit their UA, and avoid spending production on one-time-use Work Boats in the critical early game.
Zero Japan
A Fighter replacement with a bonus vs. other Fighters, and doesn't require oil. That's not too bad, but by the time Radar is researched oil resources are already online and relatively less scarce once players have secured it through CS allies or offshore platforms. Additionally, players tend not to mass build fighters in the same way they do bombers, instead putting one or two in a city to sweep and intercept. This bonus would be much more useful if this UU were moved down to serve as a Triplane replacement instead.
Flight is one of the most ready entry points into the Modern Era, coming shortly after Industrialization. If a player hasn't pursued the naval tech path, it is not unusual to get Flight first to unlock an ideology, before being forced to push through as many as five or six other techs to unlock the oil needed to actually build air units.
A non-oil Triplane replacement would effectively guarantee Japan air superiority very early on. This wouldn't be overpowering, as range is limited and they are weak vs. cities, but it would be effective in harassing nearby enemy troops and supplementing city defense, effectively negating enemy artillery.
Berber Cavalry Morocco
This Cavalry replacement receives strong bonuses to fighting in home territory and desert. I like the idea behind these bonuses, but don't think they go far enough - deserts can be small, and players fighting Berber Cavalry will know to simply move around the well defended desert areas. This bonus should be modified, so that instead of working like other combat bonuses which are determined by the tile the combat takes place on, the Berber Cavalry gets a bonus based on the territory it occupies during its turn. That is, the unit will get the 50% bonus not just attacking/defending a desert tile, but during any turn in which it has stood on a desert tile at all.
This would broaden the Berber Cavalry's zone of domination to include all territory that is within striking distance of a desert. Attacking armies wouldn't be able to merely side-step the desert; They would need to think twice about fighting near desert terrain at all. This would give Morocco a significant regional control, as opposed to a mere tactical control over a couple dozen or so tiles.
Sea Beggar Netherlands
Privateer replacement with Coastal Raider II and the ability to heal outside of friendly territory. Sadly, no player has ever looked back on a failed naval assault and said, "That would have gone so much better if I had a higher ratio of Privateers."
The healing is nice - it allows the Netherlands to protect its trade routes and control barbarians constantly without having to return to base or allied CS to heal after every fight. However, like all anti-city melee bonuses, it is at best of situational use. Melee units tend not to attack cities, they merely capture them after ranged units have worn them down, as the damage they take attacking will get them killed extremely quickly.
It's possible, with a half-dozen or so of these, to take cities effectively, but only if the defender has no Frigates to defend their cities, which is unlikely as the same tech unlocks both units. Attacking the city proper requires defeating the navy first, and the Sea Beggar has no bonus against other ships, usually requiring you bring along Frigates for the fight anyway, making the anti-city promotions needless.
Suggested alternative: Make the Sea Beggar stronger overall, and give it Boarding Party II to start instead. This would actually make melee naval warfare worthwhile for the Netherlands, as they can take out defending navies with some ease and start to work on the city, cycling out units to heal just outside of attack range. You might want a Frigate or two for attacking land units anyway, but this would go a long way towards making the Privateer useful as a competent unit that doesn't require Iron to build at scale.
Janissary Ottoman
Musketman replacement with 25% bonus when attacking and 50 HP healed on a kill. Not too bad bonuses, but they require your front-line unit be attacking to get anything out of them, which your front-line units tend not to be doing. This is the common problem with all infantry-line attack bonuses.
I would switch the 25% attack bonus to a 33% defending bonus and call it a day. Like the original Janissary promotions, these would carry over with upgrades, incentivizing the production of Musketmen and allowing for some tough blocker units.