I like the idea of characters being able to build up a library of possible rituals to really broaden out their scope. I also like the idea that rituals can be used to introduce plot and worldbuilding magics that have never fit well into D&D. How many D&D novels, adventures and campaign worlds have we seen where the magic on display is blatantly not represented by the D&D spell system?
What I am very concerned about is power and scope creep for characters with access to ritual casting. It does worry me that characters who build up libraries of potent rituals may grow to have an enormous advantage over those without. Even though they may not be usable in combat, campaign often have an awful lot of out of combat interactions and challenges. I'd hate to see non-ritual users become marginalized because the game eventually develops to the point where rituals are do-it-all, solve-any-problem answers to challenges out of combat. Or even if they represent a large portion of solutions to challenges that come up. I'd prefer it if all of the classes could contribute more or less equally, rather than having the wizard increasingly having most of the solutions as levels increase.
