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What are the pros and cons of skill trees versus flat skill lists in role playing games? In what situations is one more appropriate than the other?

Here is an example of a skill list, taken from Elder Scrolls IV: Oblivion:

Skill List from Oblivion

Here is an example of a skill tree, taken from Diablo II:

Diablo II skill tree

Some additional questions:

  1. Are skill trees inherently more complex than skill lists?
  2. Do skill lists tend to broadly cover a character's abilities, while skill trees focus on specific spells or aspects of a character?
  3. The Elder Scrolls: Morrowind uses skill lists and has a skill called Athletics that was removed in Skyrim. Do skill lists' loose coupling of skills make it easier to create useless or irrelevant skills?
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closed as not constructive by Nicol Bolas, Darth Melkor, Sean Middleditch, Patrick Hughes, Byte56 Jun 17 '13 at 13:48

As it currently stands, this question is not a good fit for our Q&A format. We expect answers to be supported by facts, references, or expertise, but this question will likely solicit debate, arguments, polling, or extended discussion. If you feel that this question can be improved and possibly reopened, visit the help center for guidance. If this question can be reworded to fit the rules in the help center, please edit the question.

Could you rephrase the question(1)? –  Dialock Jun 17 '13 at 3:50
Do you have any suggestions on how to improve it? –  Nick Caplinger Jun 17 '13 at 3:57
gamedev.stackexchange.com/help/dont-ask under Constructive subjective questions. I belive we need similar page for answers! Because if only people who have experience with it answer this question and other avoid answers starting with: "I never, but I think", it would be beneficial. –  sm4 Jun 17 '13 at 5:42
As always, although targeted at pen and paper RPG, Design Patterns of Successful RPGs is relevant to these sort of questions. –  Vasco Correia Jun 17 '13 at 12:50
This question is definitely not subjective, nor requiring textbook-lengths of an explanation. It's a fairly straightforward question with a fairly straightforward answer. gamedev closes far too many questions. =| –  Attackfarm Jun 18 '13 at 0:45

2 Answers 2

up vote 7 down vote accepted

Summary: Lists provide more agency, while trees provide more easily anticipated results that are simpler to balance and utilize in design.

To be as concise as possible, the difference between lists and trees of decisions is the level of freedom the individual making the choices has.

When speaking of skills and character progression specifically, lists such as found in Elder Scrolls provide freeform decision making. Trees provide a more guided approach, usually representing classes or sub-classes of some form. There is less freedom in character progression/creation, as the concept of a tree necessitates requirements to unlock latter levels/branches.

The freeform list provides a greater sense of agency for the player, allowing a greater number of options. The more guided tree provides a simpler system to consider and anticipate as a designer, resulting in a system easier to balance. So, the end result is that you have a choice for a potentially more balanced system versus a system that provides more agency.

To answer your edit questions:

  1. Complexity largely depends on the specifics of implementation. However, all else being equal, a freeform system is far more complex as the potential number of results are significantly higher.

  2. Yes, the traditional usage of the two is for lists to be atomic actions (such as Elder Scrolls' system) while trees are used for "Perks" or "Abilities" to simulate a focus on developing enhanced skills in a specific domain. However, this is hardly a requirement.

  3. Much changed between Morrowind and Skyrim, largely due to a number of decisions far too complex to attribute simply to "using a list-based skill system".

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+1 Good answer. –  Omokoii Jun 17 '13 at 9:15

There are no pros and cons. These two methods fulfill different requirements.

A skill tree works usually better in a scenario, where:

  • The skill points are limited,
  • Skills provide a more significant advantage,
  • The game 'feels' better, if the player characters are more specialized (the character classes / roles are easier to distinguish).

The Elder Scrolls - style skill advancement is on the other hand:

  • More realistic,
  • Encourages players to try many different approaches (the player won't have a significant disadvantage if he switches from melee to magic at level 30, for example),
  • Easier to balance,
  • Provides a feel of continuous progression (no "the best skill is unlocked at level 30 in the fire magic skill tree, I'll just try to survive until then" effect).

In my opinion, the Elder Scrolls approach is more viable in a single-player game. The player doesn't have to start over if he wants to try a different play style. In Morrowind for example, you can be an armored melee fighter for the first 30 levels or so - and then decide to try the thieving skills / quests without receiving any penalty (or having to create a new character and start from level 1).

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Isn't it easier to balance skill trees? I thought that was why most MMORPGs use trees instead of lists. –  Omokoii Jun 17 '13 at 9:21
In a skill tree, if you have to change some values of a skill (the DPS of the fireball skill, for example), you might have to adjust the whole path leading up to that skill. Or the change might 'ruin' a character build that was totally viable before the changes. I think MMORPG's use skill trees to distinguish the different character roles by 'forcing' the players to stick to one path (or their character build will be too weak at later levels). –  Marton Jun 17 '13 at 12:00
It's fairly trivial to determine and alter balanced values in a skill, whether list or tree. The difficulty in balance and design is because lists are far more emergent, and have orders of magnitudes more possibilities, which is why my answer states that lists are more difficult to balance –  Attackfarm Jun 18 '13 at 0:49

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