Hey Cal, this is Chuck, author of LoS.
It is indeed possible to "blast or heal all day" in Legends of Sorcery, *if* you are very, very lucky.
First, the DC of a casting skill check is very steep, 15 plus spell level x5. So 20 for a 1st level spell, 25 for a second level spell, etc.
Failing a skill check to cast a spell will usually result in the caster being fatigued, and then exhausted, which increases these DCs further, by +5 and +10 respectively.
So a caster will likely be able to cast low-level spells relatively freely at mid- to high- levels, but high level spells will always be dicey.
For example, a 5th level spellcaster from a high magic class (say, Wizard), could have 8 ranks in Knowledge (arcana) and would have a Base Magic Bonus of +5. Let's also assume the caster has an Intelligence of 18, for a +4 ability bonus, so a total modifier of 17.
This means the caster would need to roll a 3 or higher on 1d20 to cast a 1st level spell, an 8 or higher to cast a 2nd level spell, a 13 or higher to cast a 3rd level spell, an 18 or higher to cast a 4th level spell and so on.
If the caster was threatened in melee, raise those DCs by +5. If the caster had failed a casting check earlier in the day, increase the DCs by another +5.
Now, the example I used was at the game's MOST powerful. A 5th level spellcaster from a medium magic class, wouldn't have a Base Magic of +5, but +3. Not only would this make the casting checks harder, but his caster level would be 3 instead of 5 for spellcasting purposes.
A low magic class would have only a +2 Base Magic Bonus.
So high magic classes (those found in the PHB) are quite powerful under this system, so long as they stick to relatively low level spells.
Learning spells works similarly and has a DC of 15 plus three times the spell level (18 for a 1st level spell, 21 for a 2nd level spell, and so on).
The maximum number of spells you can know is equal to your ranks in your magic skill plus your Base Magic Bonus.
So the Sorcerer in our above example could know 13 spells. But again, this is a high magic class.
The real advantage of the system, I find, is that it allows you "dial down" magic until it reaches your desired preference.
While mid to low level spells can be cast more often, high level spells are almost always dicey.
Let's return to our talented wizard at 20th level. The DC to cast a 9th level spell is 55. He has 23 ranks and a +20 Base Magic Bonus and his ability bonus is up to +6, or a 6 or higher on 1d20 to successfully cast a 9th level spell. 11 if he is threatened in melee.
So assuming ideal conditions, even at its most extreme, he has a 30% to fail casting check. This could make all his further casting checks more difficult. For example, on a natural 1, the caster would be exhausted after casting 1 spell, increasing the DC of all his casting checks for the rest of the day by +10.
If the caster was threatened in melee and rolled a natural 1, he'd suffer 9 points of damage, be exhausted and the spell would have a 25% chance to go off.
In medium magic campaigns, those rolls would need to be 5 higher (11 or 16 if threatened in melee), in low magic campaigns, 10 higher (16 or 21 if threatened in melee).
In short, I think the LoS magic system brings a lot of flavor to the mix. I makes spellcasting riskier, and makes it easier for the game master to construct low and medium magic campaigns while still using the spells found in every known d20 product.
Hope this helps,
Chuck
