It's a spell point system, but with chunked points or mana. You have "Spell Slots" of various levels and use them to pay for spells. Once these power tokens are spent, you are out of spells.
SpellbookLet's start at the beginning. Like classic games, you have a spellbook and can put any spell in it. Adding a spell to your spellbook takes 2 hours and 50 gold per level.
Spell PreparationThen you pick a list of spells to prepare. You can prepare a number of spells equal to your level + Intelligence modifier. For a first level character that is likely 4 spells. For a fifth level character, that is likely 9 spells.
You never lose these spells. They can be of any level and any combination. You could pick all first level spells if you wanted, or any combination of spells that you know.
Cantrips, of course, are at-will powers. Light, Ghost Hand, 1d10 flame burst (2d10 at 5th etc.)
CastingTo cast a spell, you use a spell slot equal to the level of the spell. But wait! There's more! Spells never increase in power based on your level. Do you want to do more damage? You have to use a higher level
Not many. A first level caster has 2. A third level caster has 4 first and two second. You never get more than 4 first level spell slots. You never get more than three second to fifth level spell slots.
So fewer spells, right? But a close reading of the rules indicates that you can no longer interrupt spellscasters. If a spellcaster uses an action to cast a spell, they are going to get that spell off -- there is no way to stop them.
Ready an action you say?
"When the trigger [for the readied action] occurs, you can either take your reaction right after the trigger finishes or ignore the trigger. Remember, you can only take one reaction per round."
The only detriment to casting spells in melee is that you have disadvantage on a ranged attack roll. No attack roll? Casting a melee spell? No problem!
However, it's not all bad. . .
Many, many more spells require concentration. While concentrating, you can move and attack and cast spells -- as long as you don't cast another concentration spell. If you get hit, it could dispel the concentration (You must make a constitution save vs. DC 10 + 1/2 damage dealt, which is actually a pretty difficult target to hit). Also, it ends if you die.
Here are a list of all the spells that require Concentration:
Antimagic Field, Arcane Eye, Beacon of Hope (Advantage on Wisdom & Death saves, max hit points regained from healing), Blade Barrier, Bless, Blur, Dancing Lights, Darkness, Delayed Blast Fireball, Detect Magic, Dominate Monster/Person, Earthquake, Find the Path, Faerie Fire, Flaming Sphere, Fly, Gate, Globe of Invulnerability, Greater Invisibility, Guidance (+1d4 to ability check), Haste, Hold Person, Holy Aura (Advantage on saves, Opponents disadvantaged on attacks), Invisibility, Levitate, Locate Creature, Magic Weapon, Major Image, Maze, Mordenkainen's Sword, Otto's Irresistible Dance, Protection from energy, Resistance (+1d4 to a save), Shield of Faith, Silence, Silent Image, Spider Climb, Spirit Guardians, Stoneskin, Suggestion, Wall of Stone, Web
No more than one of those spells can ever be active for a single caster*. 43 out of 126 spells or over 1/3 the spell list (34%)
No more flying invisible wizards!
No, It's the Same Magic Missile
The other major change is that the power of the spell no longer increases with caster level. Magic missile fires 3 darts that always hit a target doing 1d4+1 damage each at level 1 and at level 20. You want more darts? Use a higher level spell slot.
This is true for most spells. Want more targets? Use a higher level slot. Some spells allow using a higher level slot to obviate the need for concentration (but very few).
However, cantrips can increase in power. A Fire Bolt does 1d10 fire damage within 120 feet on a successful attack roll (Proficiency + Spell-casting stat). At 5th level it does 2d10. At 11th? 3d10, and all the way up to 4d10 at 17th. No higher level spell slot necessary. Evokers even get to add their Intelligence modifier to the damage after level 10. At level 14, if you are an evoker, you can overchannel the cantrip! The other cantrips, Ray of Frost and Shocking Grasp are similar, but do 1d8 damage and have a special effect.
Does it Get Results?
Wizards are difficult to balance. And I don't mean in that "Everything has to be fair" sort of way, but in the way where people can play at the same table with the wizard and feel like they can contribute solutions besides helping the wizard pick which spell to solve the problem.
Concentration quite aptly deals with the stacking buffs issue prevalent in 3.X/PF. It requires them to make choices. They have more flexibility and staying power due to cantrips and the fact they spend slots to cast what they have prepared. Their very existence obviates several factors of old school play (Light at will, Ghost hand at will), but this isn't a game made for me. This is a game for 12 year-olds and up, who after a lifetime of Harry Potter, have reasonable expectations that wizards can fling bolts of whatever around pretty much at will.
I'll have more to say after I play the game a bit. Feats also might provide interesting options for Wizards, we will have to wait and see if they dominate the game to the degree they have in the past.