What are the best spell systems as far as you're concerned, the best way to handle magic in a fantasy setting; and what characteristics do they have that make them so enjoyable to you?

I love how they handle spells in WFRP 2e.  You can cast as much as you like, but you run a risk of going nuts at low levels, or having everything explode in your face at high level.  So magic can be incredibly powerful, but its also always gambling with your life.

RPGPundit

I've always been a fan of Ars Magica's verb+noun in latin as skills and combining them allow you to make spells on the fly. One of the first magic systems that I found really effective and flavorful. especially since spell durations read like folktale/faery tale terms "until sunrise" or for a year, or until the sun sets over the mountains...and so on.

Quote from: SilverlionI've always been a fan of Ars Magica's verb+noun in latin as skills and combining them allow you to make spells on the fly.

Yup, the magic system in AM is a classic piece of game design. I also enjoy the later mechanics which it has so clearly inspired: magick in Mage and miracles in Nobilis.

I really like the magic system in Buffy.  Less so the attached telekenisis system which is somewhat clumsy but the magic system is great fun and beautifully designed as well as perfectly in genre.  I think it owes quite a bit to Ars Mag too, being semi-improvisational.

I like the magic system in 1st ed. Pendragon. It's GM special effects. No, your PC knight cannot cast spells. They added a magic system in 4th ed., but while it's elegant and atmospheric, it's entirely unsuitable for PCs.

I like the magic system in HeroQuest. Your magic abilities, like all other abilities, are described by a word or short phrase. How you use them in play is negotiable.

I'm all about Power Points.  I like how Rolemaster does it--1st level spell=1 PP, 3rd level spell=3 PP, and so on.

Ars Magica, hands down.

Plus, if you wanted a game less about the magi, you could add a fatigue/health cost, or a power points system, or require vis to be found - similar to the charges system from Unknown Armies.

On that point, Unknown Armies - only a madman believes magic works.  And thus, only a madman can use it...  however, I can't remember the actual mechanics for learning/inventing spells...

V.

Ars Magica, of course. Green Ronin's True Sorcery, which is the system introduced in The Black Company campaign setting. I also like the system in Decipher's Lord of the Rings RPG. That system is similar to D&D's system, but it has a simple fatigue system instead of spell slots.

Elements of Magic: Mythic Earth

Takes time to learn, but once you have it down you can create all sorts of spells.

Ars Magica

What they said.

Dangerous Journeys: Mythus

Tons of spells, spell use requires skill, spell selection requires a modicum of good sense and planning ahead. The spell design rules are clunky, but you do get a shitload of spell effects you can incorporate.

Speaking of the last two. Somebody modified the spell creation system in Ars Magica for Mythus. Unfortunately it's no longer up.

True20 Based heavily off of Steve Kenson's Psychic's Handbook.  No spells, a series of skills and feats (which are mainly buy in to get skills).  No slots, points, or hard limit on how much magic you can do, just likelihood and fatigue.

BESM 2e actually 2 systems.  The first is ok but, like most free form systems, it boils down to "we don't have any real advice, just make it up as you go"  The second one does "you know all the special powers that make up half this book?  Use any of those to fashion your own spells."  Then it  reduced the cost for those powers with the tradeoff of tapping into a limited resource.

Another vote for WFRP2 magic here. In mechanical terms it's very simple to handle, which is good. What I also like is that it makes magic a force to be reckoned with instead of just a resource to be managed. I like this.
 
So far too the system's working well in my game, although the Apprentice Wizard PC is still only casting '1st level' magic, which means that I've yet to see the how the system works out at higher power levels. But the elegant simplicity of the core system is such that, when magic made its initial appearance in my game, it was a genuinely memorable moment in which the quiet elf revealed her true potential- ie. it was dramatic, instead of just being a moment in which a PC's special powers were first crunched-out. I liked this too.
 
I also quite liked GR's True Sorcery as a logical design. It looks like it could be a bit of a bitch to use in practice, but I liked the way it was done.

I've read too much Conan as a kid, and so I never really liked magic in my games.  This change with C&C.

I know it's D&D's magic system, but C&C is what made me think about it again.  I strarted thinking about how it would work...and in making magic such an arcane, creepy thing, it added a whole new feel to "fire and forget" spells.

C&C really made me enjoy fantasy again, and renewed my interest in D&D style fantasy...and it is the magic that did it.

Quote from: Zachary The FirstI'm all about Power Points.  I like how Rolemaster does it--1st level spell=1 PP, 3rd level spell=3 PP, and so on.

I like Rolemaster as well.  The Spell List is a great tool to easily build spellcasters with themes.

Call of Cthulhu's system is simple and most spells are delightfully unique.

I like the Magic systems in the Iridium System the best, or ones like it.

Here are the three main ones:

Spell points
Free Form
Mix of the two above.

I'm surprised no one has mentioned Midnight or Earthdawn.