I don't really understand the motivation behind a system that prevents characters from learning the basics of skills after they reach certain proportions of levels or other skills.

For example, with Fallout, what would have happened if the speed at which you gained levels was always the same, regardless of what level you were at? Your skills would have grown out of control near the middle of the game. To remedy that, the game just needs to severely reduce the number of points to spend on each level. The cost of increasing skills was already set up to be more expensive as they get higher. That already provides a crossroad to generalization and specialization.

So now the only difference is that characters can upgrade really bad skills to decent ability after they nearly max out their important skills. They can even max out all skills, if given enough time. But by the time they do so, most would have already stopped playing the game anyway. In Fallout, there was a point where leveling got slowed to such a crawl that I no longer considered it part of the gameplay.

The only negative consequence that comes to me is that replay value is diminished, since players can master all skills in one game. But there are ways to compensate. Fallout's primary body statistics is one, since you generally have to start a new game to have a different set of stats - a different type of general character. And any type of skill setup where the player can only choose one of several abilities at each junction is another way to bump that up - similar to the Deus Ex augmentation upgrade cannisters.

I think you should try to avoid making a character that masters everything feasible, though. It happened in Fable and got very boring (for me) that I could do absolutely everything, and I didn't sacrifice anything. I'm not saying don't allow it, just make sure the numbers work right so someone who fights a little more doesn't *always* become that uber-monster of DOOM. Mostly make sure the game isn't longer than the levelling system, or that the experience needed for each new level of power don't come too fast, so that at the end, the character is amazingly amazing.

Assuming that makes sense, good luck!

Players that devote enough time to enhancing all of their skills will be able to master just about everything. But if they're playing to win the game, they probably won't fully max out even one skill by the time they finish the main quest (unless, perhaps, if they develop only that skill). No skills will need to be enhanced beyound moderate levels to finish the game.

However, there will be many optional objectives that will be far more challenging than the main quest. In some cases, the optional quests will even have a more meaningful end-result than the main quest. Truthfully, the main quest is only there for players who have a hard time finding their own way.

Imagine playing The Sims, except to win the game, you just need to walk from one street corner to another. The plethora of interesting things you can do before reaching the end is where the game actually exists - developing your sim, building the perfect house, whatever. The main quest will be more lengthy and meaningful than a walk down a street, but that works for the analogy.

I was considering using some type of skill degradation / deterioration. I've heard Ultima Online did that. However, my game is single player. It isn't really meant to be played for years and years as with an online game. I haven't decided one way or the other.

Since you're sort of letting players "purchase" their skills/updgrades, it wouldn't hurt to allow a sort of buyback thing, that allows them to sell their skill for some experience back. Or have a trial run, where the longer you've had a skill, the less % of your spent points you can 'buyback'. Especially if you have many skills, it'll allow a player to figure out if they like THIS skill, before permanently spending 4+ hours of experience on it, or something similar.

I think that's actually a phenomenal suggestion dekasa, maybe have a time period of 1 hour in which a player can sell back their upgrades for 100%, so it becomes a test drive of sorts. I think this would add to the flexibility of the skill system, and seriously reduce buyer's remorse, since if you end up buying a skill/upgrade that you really dislike you will be able to get rid of it again with little to no loss.

In my own game, the skill upgrades for most stats will be minor increments. Not enough to implement a sell-back system.

Personally, I've also always found that the risk involved with upgrading stats is part of the appeal of character development. If the character development itself is supposed to be part of the gameplay, then shouldn't tweaking the perfect warrior be somewhat challenging? That doesn't mean the stats should be cryptic or misunderstood, but I think test-driving would be taking it too far in the other direction.

Yup Kest.

Frankly, I played Fallout couple of times from beginning to the end, trying various character growth path to 'try out my own battle styles', and frankly, most of other single play games, too, class based and non-class based altogether.

Non-class based multiple possibilities mean one of two.
1) (Easy balancing) Become a superman
or mess up the skill tree but endure, manage to watch the end
or mess up and restart
2) (Hard balancing) Become an okay character
or mess up the skill tree and restart

Although there isn't any square partitioning of character classes, finding it out itself would be another pleasant entertainment. (lest players suddenly remember the 999 useless dungeon vacuuming and never do it again - that's what we call a 'single experience is enough' boring game)