So the biggest thing I like about 5th edition (from the free online PDF anyway) is the idea of ritual spells.
To summarize - using the same spells/day magic system we have in pathfinder but reducing the # of spells per day drastically - however many spells have a new 'ritual' tag. These spells can be cast without having to memorize them, with the caveat that they take 10+ minutes to cast.
I like this thought - this makes *all* the spellcasting classes a bit more versatile and allows the idea that some spells/magic/'stuff' should generally always be available to a party outside of combat - which changes the idea of how to build encounters and adventures - with the idea that given some time the cleric can always ask for some advice from their deity - or that the wizard can always setup a circle of protection if given enough time/etc.
Also by limiting the # of slots for 'combat' use the casters are made less 'god' and reigns in the power creep - although I don't have any practical knowledge of how this plays out at higher levels.
I'm interested in what other people think of this system, vs other attempts at changing the caster progression that have been attempted.
Ritual magic is something that I think is sorely lacking from Pathfinder
It's not quite the same but Kobold's Deep Magic includes Invocation Ritual Magic. Basically a reworking of Invocations from the old 3.5 Unearthed Arcana with some additional material.
The 5E Ritual system is handy since it saves on spell slots when it comes to a lot of situational spells;"I don't need to prepare a Knock spell unless it's something I'll need to cast in a hurry. I can just use the ritual so long as we have a few minutes or so to spair." It fills in where PF and 3.5 players would be buying a collection of Scrolls instead.
Invocations on the other hand are a lot more conditional and specific. They work very nicely for thematic reasons as well.
"I must perform the Invocation of Doom on the eve of my birth with the aid of a dozen lesser wizards and the Blood Sacrifice of a Demon-Possessed Platapus. And with it's completion my undead hordes shall be unstoppable"
I tend to prefer rituals for bigger spells; but then, I mostly think of rituals in cases where I'm, say, planning E6. There's no way you can cast earthquake if you're not going past 6th level. But maybe you and a few buddies can cast it over the course of an hour.
That's the sense I tend to prefer rituals in, but it's also good for smaller spells; it doesn't chew up those combat resources, and it doesn't have the advantages over mundane methods like being a standard action instead of a minute to pick a lock.
I didn't like the 4th edition approach because every ritual cost money for each and every casting, which seemed to me like it would make it hard to justify using rituals regularly. If you have alarm, you want to use it nightly, but the costs add up pretty quickly.