How do you want your character's power level to increase as you play an RPG? This post is intended to explore different options.
I've always considered increasing my character's power (i.e., experiencing vertical power progression) an important and rewarding part of the genre. I might start outside my home city with a rusty sword and a couple of basic skills, but I don't want to stay that way forever. I want to explore the world and fight monsters, gaining new skills and better gear along the way. Eventually, tasks that were impossible at the beginning become doable. By gaining power, I unlock more opportunities in the game.
But how fast should a character gain power? And should the rate of improvement change as time goes on? Here are some options I've seen...
Option #1 - Linear with Cap
With this method, character power increases steadily until progress stops. This is usually achieved by means of a level cap. Characters might still be able to improve in some ways (e.g., learning how to do different types of damage) but their absolute power level is limited. Guild Wars 2 is famous for this style of progression (though I can't say I've played it).
Option #2 - Linear Forever
With this method, character power increases steadily forever. Games like this do actually
exist, but the method doesn't lend itself well to an MMO because new players will be hopelessly behind. However, this could be remedied via level boosts or other catch-up mechanisms. Content creation would have to be very fast (probably automated) to continue providing players with challenges.

Option #3 - Exponential
This method starts with slow power gains that gradually ramp up. This is generally considered un-fun and reserved for real-life investment banking.

Option #4 - Asymptotic
This method provides strong growth in character power early on. Improvements are fast at first, but then they slow way down. Character power approaches a limit that it can never exceed. This is like EVE's system for faction standings. Note: You could modify this method slightly to produce logarithmic growth instead. That gives a similar graph but doesn't have a hard limit.

Option #5 - Stop and Go
Any of the previous methods can be combined together. This is how WoW's expansions worked for a long time (at least until I stopped paying attention). Each expansion opened up a new level of power that greatly exceeded the previous expansion's. Old content becomes trivial and often obsolete.


So what do you think? Which system would you like to see in Ashes of Creation?