My thoughts on some things that need improvement in the ruleset as I experienced it in LT51:
Economics
- Gold-multiplier buildings come too fast too early. Markets are good as they are, but Banks come rather soon afterwards, and Stock Exchanges come WAY too soon. Why is this a problem? It means that nations experience an "Industrial Revolution" of sorts long before Factories and Power Plants. Gold buys gold multiplier buildings, which buys more multipliers and happiness buildings to support max-food growth, which then finally culminates in a mass-purchase of Libraries and Universities to begin a massive tech rush. This greatly enhances the powers of Farming, and of sacrificing everything in the name of food, and the trade that results from the population growth. Early Stock-Exchanges also make it too easy to Celebrate.
- Democracy is a very powerful government. Not only do you get a strong celebration bonus, but you're immune to Bribery and Incitement! I scarcely saw another government this game besides Fundamentalism and Democracy. Both, not coincidentally, are immune to Incitement. The one notable example I saw of a player not using one of these governments switched from Monarchy to Democracy after I bought all the cities on one of his islands.
- The Great Lighthouse small wonder is badly overpriced for what it does. Although getting veteran Triremes is nice, at 200 production it costs nearly as much as 7 triremes! If you're fighting an early battle for control of the seas, you can't afford to build it. By the time you CAN afford it, the age of Triremes is over as anything but a specialized river-boat. And the movement bonus? +2 movement is nice to have, and it gives it to all of your ships...except Triremes!!!. Those only receive a +1 bonus unless they are feeling brave enough to actually sit around on the open ocean for a turn. Reduce the price of this wonder, and remove that ridiculous exception for "not starting on the ocean".
- Unit Upgrades are too cheap. I know they still cost a lot of gold, but it can be mathematically proven that it is better to rush-buy a mass of Warriors or Horsemen and then upgrade them to Muskets or Cavalry later. This does lead to an interesting strategic gambit of "how long should I invest in obsolete units before I upgrade them into a modern army?", but it comes at the cost of being totally stupid on one critical point: It gives you a dis-incentive to research modern weapons! When you research Feudalism to build Pikes, you say "oh no, I can't build warriors any more!". When you research Chivalry to build Knights, you say "Oh no, I can't build horsemen any more!". This is stupid. Technology should help, not hurt.
- Knights are useless. By the time you can get them, Pikemen are available, and gunpowder is just on the horizon. Knights aren't even a strength upgrade over Chariots, just more flexible. A pity that they are obsolete as soon as you discover them. Made worse still by the fact that researching Chivalry denies you the ability to build cheap horses for upgrades, and you have a unit that you're literally better off without. Give them 5 or 6 attack. Give knights teeth.
- Island warfare is pretty boring in the early/mid game. If your opponent has their rivers protected from your Triremes, and has covered all of the mountains/hills that you could try to unload on, your options for attack and harassment are basically non-existent. There should be at least SOME "can attack from non-native tiles" units available in the early game. They don't have to be powerful, but there should at least be the option to attack weak targets and seize landing points.
- Transport ships are very very powerful. Not sure if this is a problem, but their extremely high movement speed allows for powerful actions of strategic surprise. Warships are nearly useless in comparison. If a stretch of water can be covered by a Trireme/Caravel/Galleon/Transport in a single turn, then all of the navies in the world won't be able to save you if your opponent has a way to unload an attacking army in your land.
- Siege Units are nearly useless on islands. Certainly so for attacking cities. They were mainly used for sinking ships foolish enough to wander close to shore. Why can't they help attack cities? BECAUSE YOU CAN'T TRANSPORT THEM. Not until the modern era, at which time they are nothing more than cost-effective ammunition for grinding down cities in an invasion. The fact that Galleons can't carry Cannons is a bit ridiculous. At least let Galleons be useful as more than just "bigger faster caravels". Now, granted, this will turn Transports into "Bigger, Faster Galleons" by taking away their qualitative difference, but you need siege transport ability sooner in order to make the game interesting.
- Frigates are Ridiculous. They are very nice units in the power they open up to raid coastlines and murder pre-gunpowder units, but their 4 attack is paired with an absurdly low defense strength of 2. TWO!!!! And there's no defensive terrain to offset this. This means that naval warfare with frigates becomes purely a matter of who attacks first. Can you imagine fighting a land war on pure flat plains with nothing but Horsemen? yeah, that sounds pretty terrible. And yet that's what the entire Age of Sail is. One giant game of "rocket tag".
- Ironclads are useless. Their stats are identical to a slow Frigate except they are provided with a luxurious 4 defense. Wow! That's what a Frigate should have had in the first place, but now you have that in a unit that: Comes later, Costs more, Moves slower, and will soon be obsolete. And they're not any stronger! A Frigate vs. Ironclad battle is a 50/50 fight. Ironclads can't attack any better than a Frigate, and can't defend well enough to be able to protect shipping. Both ships upgrade to Destroyers. If they came from the same tech, I'd prefer the Ironclads to the glass-cannon frigates, but as it stands, there's basically no reason to build Ironclads. Raise their Attack and Defense to something higher. 5A/5D?
- Artillery is underwhelming. Sure it's better than Cannons. But not by all THAT much. 10 attack power for 60p vs. 8 attack power for 50p. That's only a marginal improvement, and hardly the level of benefit I would expect from a unit so high on the tech tree. If it didn't lead to other techs, I might not even bother. Give it 12 Attack, make it be a real upgrade.
- Cruisers have 2x Defense as their Attack! I'm not complaining, I like this. Imagine the possibilities...being able to actually defend things on the open ocean. Is it too much to dream? Or was this a typo and they were supposed to have 8 Attack instead?
- Forts are extremely powerful. Preventing stack-kill is good, but also doubling the defense of the tile (multiplying with all the other defense bonuses) makes units in a fort nearly invincible. Their only weakness is that as a form of Static Defense, they can be bypassed, any if the supporting cities of the units die, the fort is abandoned. I'm still uncertain how I feel about them. Overpowered or Inconsequential?