Derek can you explain why you guys did not seperate the Tech trees? What I mean is that there are some techs who's pereq's are from a different tree.
Personally I wish you guys would have either keeped them seperate (Ala. Endless Space) or just have one tech tree (ALA. many 4x games CIV for example.
Having cross tree dependencies means that we effectively have 1 tree. That we display it on 3 screens is just a UI/flavor choice. It helps guide players into thinking about the 3 different types of research they can be doing, and we have some fun with it on knowledge trading (which is separated by type of research). It ties to the 3 city types, etc.
Conceptually I like the idea of 3 separate tech trees. But that leaves you unable to provide the late game cross tree benefits that combines resources can do. I can put unit upgrades in one tree and group sizes in another. That works out well since they are multipliers and advancing in both trees makes your trained units better without linkign the trees with prereqs. Thats the correct way to do it.
But then you have things like enchanted weapons. You dont want the magic tree to own them (without prereqs) because then you ignore military and tech up the magic path to get the best weapons in the game. You dont want the awesome enchanted weapons to just be in the military tree because it fits so well thematically with the magic tree and its everything the magic tree is supposed to own (ie: crystals, enchanters, magic items for your units, etc).
So you have 3 choices.
1. Use prereqs, but try to use them as little as possible. This is what we opted to go with.
2. Have the item itself require 2 branches (so the enchanted axe requires weaponsmsith and enchantment, but the techs dont require each other). This is what the original design called for. The problem is that its confusing to tell when you unlock certain things. If I tell you an enchanted axe requires weaponsmithing and enchantment it seems reasonable (so it sounds simple). But taken as part of a big process it gets confusing. What tech in the tech tree do we show that item on? How many times will players unlock one tech or the other and not understand why they didnt get the item? In the end it was more intuitive to the player to create a new tech that required both techs and place the items there, rather than try to accomplish that same effect at the item level.
3. Dont ever grant perks that are tree combinations. In this case we wouldn't have enchanted battle axes. Instead we would have the magic tree unlock accessories that added fire damage (or whatever) to your weapon so that your best attack was from getting the best weapon and the best magic accessory to boost it. This is the cleanest design and would be great for most games but we can model and show all those cool weapons. I dont want the late game unit with the best possible axe to look like he just has a battle axe. I want it to be on fire, to engulf the victim in flames when it hits (this was added in beta 5). So we have enchanted axes.
If you are thinking, why dont you just have the system apply flame effects and stuff to weapons so you can use the base weapons so we can switch them dynamically. That would be cool. But we dont have that tech. It also opens up multiple issues (what if you have something that gives bonus fire and bonus cold, does the weapon play both?) Does every weapon in the game need to be keyed for the procedural application of these effects? what are the chances it will look good on them?
And thats just for the weapon example when we are discussing cross tree prereqs. But thats basically why I decided to use cross tree prereqs (though as sparingly as possible).