Some pen-and-paper games lay out everything for you and make your choices for your character as you level. You get a level, and the system says you get X and Y powers, ability scores, and hits. These are planned systems, and some good examples of them are:
- d20, Pathfinder, and D&D
- Basic Fantasy and Labyrinth Lord
- Fantasy Age and Dragon Age
- Most class-based systems
- Most MMOs
Some pen-and-paper games are DIY (do it yourself) games, and often these give you a number of "character development points" to use anyway you would like to improve your character. Some examples of this type of game include:
- Savage Worlds
- Legend and Runequest
- GURPS and Champions
- Mongoose's Traveller
- Star Frontiers and many of the TSR Boxed Games
- Most classless systems
And some fall in the middle:
- Fantasy Flight's Star Wars System
Planned systems are great for newcomers, because it is a lot easier to say "you get this and that" when you level instead of spending time sorting through the rules and the book asking the question "is this a good choice" over and over again. Believe us, we have been there, and you practically have to teach every new player the complete set of rules when they first level up with a DIY system. Otherwise, how would they know what is good?
Planned games protect new players from making bad choices, and balance the game based on prebuilt and predictable "endgame" builds.
We prefer DIY systems, because we like making our own choices when we progress characters, and we are more experienced players who know what we want when we build characters. Some planned systems have elements of choice (skill points and multiclassing), but a true DIY system foregoes classes and balances the game around skills and task resolution. Personally, when I level a character, I don't like feeling limited to the choices the game makes for me, especially if that wasn't the direction my character was going in during the last adventure.
If my warlock spent most of the last session socializing and roleplaying, why should he advance in "warlock power" at the end of the night? Shouldn't something reflect his learned ability in socializing and people skills due to this experience?
With a planned system, it is difficult to reflect those experiences and often you end up a better warlock and just as bad as a talker as you started. Warlocks aren't talkers, are they? That's a bard! So do I have to take a bard level now? Great, hand me a lute and paint it black.
With a DIY system, I put some skill points in a social skill reflecting what I did that night, and I am done. How did I get those XPs? Shouldn't those reflect my experiences? My warlock powers don't increase because I didn't use them, but who cares? If this campaign is all about talking, I am all setup for the next game with a little better oratory skills under my belt for next time, and I am happy. If next time we have a swashbuckling adventure I may pick up a sword skill or two.
Does it matter I am not progressing along a game designer's pre-planned class advancement track? Something the company spends countless hours balancing and tweaking to get "one" advancement experience perfect? No, it doesn't. My "advancement track" is the adventures I go on, and if I end up more of a glib, sword swinging practitioner of dark magic than a pure 100% power-level don-nothing-else factory-stamped-out warlock I don't care. My guy is my guy, and the adventures he went on made up the skills and powers he collected along the way.
DIY systems focus on organic advancement and balance the game on skill rolls and task difficulty.
DIY systems don't really have predicable "endgame" character builds, you just become very good at doing the things you do the most. You may end up the world's best talker, but if that is what you enjoy having your character do at the table, that is a good thing since your character advancement reflects what you are doing when you play.
Planned systems also tend to have these "pre-balanced" endgames, where the fighter will always have X attacks at Y to-hit, and be able to do Z damage a turn. Since the game designer "planned" this out, relative character power between classes is easy to calculate, and the "end game" monsters are easier to balance, Well, they should be, but a lot of planned systems typically don't take a lot of factors and exploits into consideration at the higher end (conditions, initiative, and turn denial powers) and things fall out of balance easily.
This is why a lot of competitive multiplayer online games are (or end up being) planned systems. You saw this in World of Warcraft's evolution, a lot of DIY systems were dropped to put characters in predictable, damage-and-healing-output-known envelopes. PVP and PVE balance in these games equals challenge and fun - at the cost of letting you level up your character how you choose to play.
D&D 4 was like this for us, at the high end the game fell apart for us because of the amount of stuns and other powers that rendered foes unable to act during a turn, and also our characters felt like they were getting competitively weaker versus the monsters they faced. The end-game tactics broke down into: go first, deny the enemy his turn, load it up with conditions, and beat on it with "whatever power you have" until it succumbs. The game wanted to be battle chess (which it was for us at low levels), but the high-end game did not work - at least for us.
With a DIY system, the endgame can be calculated if you do a little math, but the end-result is typically a flatter power level. The numbers usually don't get way out of balance, as the system is usually balanced around task resolution. Better skills can lead to a higher DPS and damage output in a DIY system, since you are hitting more and you may have access to special combat moves and abilities you purchased with your points. The Star Wars RPG by Fantasy Flight does a good job with talents and making those unlock higher levels of combat power, so there can be a calculated "end game build" with a DIY system - it just takes a little more design and forethought.
What character advancement system you like is of course, up to you. There are times when "I don't want to think" and I appreciate the simplicity of a planned system. I still like Fantasy AGE a lot, and I feel it is a great, stepped and balanced design that does a better job at planned advancement than most d20 based games. It is a more modern design with a hybrid "choice plus planned advancement" that I like, and it is a fun and simple model and great for new players. One problem with this model is that if the game designer doesn't think of a role, it is not viable - such as Dragon Age vs. Fantasy Age and the rogue archer issue.
We still like DIY advancement systems for our games, since it fits our play style better. We run wide and diverse games, and they don't always fit into the box of a planned class box that easily. For us, what happens at the table that night is how the characters advance, and if the players want to go sword swinging and combat one night, they can reward themselves with those skills at the end of the night and get a little better. If all we do is roleplay and socialize with NPCs, that is what is rewarded at the end of the night. It fits how we play and gives us a better sense of satisfaction when players figure out rewards, and it also reflects how we play and what happens around our table a little better than a planned system could ever account for.