I'm not sure everyone in this thread understands how spell slots are used in 5E.
Wilma the Wizard, 7th level with a 16 Intelligence, can prepare 10 spells after a long rest. (Number of spells she can prepare = Wizard level + Intelligence Modifier)
Those 10 Spells must be in Wilma's spellbooks and must be of a level she can cast.
Let's say she prepares: Magic Missile, Feather Fall, Shield, Expeditious Retreat, Levitate, Invisibility, Misty Step, Fireball, Haste, and Polymorph.
As a 7th level Wizard, Wilma, has a set number of spell slots she can use:
4x 1st level
3x 2nd level
3x 3rd level
1x 4th level
Wilma could, if she so desired, use all of her 11 spell slots to cast Magic Missile 11 different times. (Using higher level spell slots would give her additional missiles for extra damage)
After she cast 11 Magic Missile spells she would have no more spell slots left.
Instead of 11 Magic Missiles she could have cast 2x Shield, 1x Feather Fall, 1x Magic Missile, 2x Levitate, 1 x Misty Step, 3x Fireball, 1x Polymorph.
This would also use up all of her available spell slots.
Once Wilma has used up all her spell slots they would be gone until Wilma finished a short or long rest.
After a short rest, once per day Wizards can get back spell slots equal to half their Wizard level rounded up, in Wilma's case 4.
She could choose to get back 4 1st level slots or 2 2nd or a 3rd and a 1st or a 4th)
All of her spell slots would be restored after a long rest.
Even without any spell slots Wilma could still cast any of the 4 cantrips she knows an unlimited number of times as cantrips don't use a spell slot to cast.
It's a flexible system but I don't think Swen Vincke is out of line when he called the system unintuitive.
