There's an interesting game design choice 5E does different than previous editions as far as spellcasting goes. There's three significant gameplay effects that come from what they've done compared to previous Vancian magic systems:
Low Level Spell Power
In older editions, there were some low level spells that would grow in power - Magic Missle, for example. You'd do a lot more damage with it at higher caster levels, but it was still a 1st level spell slot to use. So a 1st level spell became deadlier with your character leveling up, stacked on top of all the other magic power you were getting.
In 5E, what happens is a 1st level spell only gets more powerful if you use a higher spell slot to cast it - it's not automatically more powerful, but you DO get the flexibility to make it powerful - at the cost of being able to cast a higher level spell.
Prepared Spell Planning
Previously, preparing spells was pretty much the difference between useful or useless as a character.
Let's say you can cast 3 spells of 1st level power. And you prepare Magic Missle as one of them. You cast the spell. Later on, you really need to cast Magic Missle again - too bad! You used up the one and only memorized casting of it you had. You had to plan how many multiples of a spell to prep if you thought you might need more than one. If you guessed wrong, you basically had a useless character for that game day.
In 5E, you prep a list of spells you can cast, but you can assign the number of spell slots to cast them in any way you want, provided you meet the level limits. So, if you need 3 Magic Missles that day, you can spend all of your castings on that. If you need 3 Sleep spells, you can do that, instead.
You plan ahead the general load out, but the specifics within that loadout, you make the call as you go.
Low Level vs. High Level Spell Competition
Finally, because of that set up, you have to make some interesting choices about your prepared spell load outs - you will have to decide how many spells to prepare of what kind of level - do you have more flexibility with lower levels spells, or higher level spells?
Lower level spells can often also be cast at higher levels, so there's a flexibility in power, to that. On the other hand higher level spells give you access to certain effects you can't get any other way. If you've only got 1 or 2 high level spell slots, maybe you want some flexibility in prepared spell options so you can use them the best way possible.
All in all, the new system still rewards strategically considering which spells to prepare, but isn't overly punishing or forces mages into a binary of useful/useless. There's some mild effects that look like they're aimed at somewhat curbing the "quadratic wizard" effect, though I'm guessing we'll have to wait until the full rules drop to say much of anything about the whether that actually happens.