At the beginning of this month, Gavin Norman of The City of Iron blog made a couple of posts about the necessity of the classes in 5E, and how the "subclass" options of each of the non-4 core classes could be reassigned to the core 4. I'm starting to think he might be right.
I've gotten involved in a PbP 5E Arena game on RPOL.net. So far, we've gone through a short series of combat encounters as Level 1 characters, and now we're jumping to level 3, which is when every class now has a special subclass path available (a few classes get them earlier). I played a Halfling Barbarian, but now I'm thinking of switching to a Magic-User class (Wizard, Sorcerer, or Warlock).
There's not really a whole big difference between the three classes, since they all are focused spellcasters, and they have very similar spell lists. Mainly the differences are in the fluff associated with the classes, and the mechanics they use to gain/prepare/cast spells.
Wizards prepare spells from books, classic Vancian magic. They specialize into schools of magic, gaining greater proficiency when casting one school's spells, and some related abilities.
Following 3E, Sorcerers have innate magical ability. They only know a handful of spells, but can use a special reserve of magic points to cast more spells, or modify their spells with metamagic effects (greater effect, greater range, silent/still spells, quick spells, etc.). They can either gain some "draconic" heritage traits, or be "wild mages" (yeah, old school style random effects going off!).
I'm planning to rebuild the character as a Half-Elf Wizard, and I think even with the less than optimal racial ability score adjustments, he'll be more powerful (and for an Arena game, there's no reason not to Min-Max).
When 3E came out, I immediately liked the concept of the Sorcerer. They had the same spells as the Wizard, but could cast MORE spells per day, although they had a more limited repertoire to draw from. The weakness of the class design was that they were otherwise identical to the Wizard, so suffered from poor skills (Wizards got 2 from the class itself, but since Int was their primary ability, they were guaranteed to have plenty, whereas Sorcerers use Cha to cast, so Int was a dump stat and they only got the 2 from class, for example), poor hit points, poor armor class, etc.
Wizards got versatility from being able to fill up spellbooks with as many spells as they could buy, beg, borrow or steal. Their limits came from having to select their spells in advance to fill their more limited spell slots. They also got bonus feats for metamagic or item creation feats.
Now, in 5E, it's sort of been switched around. Sorcerers get easy access to metamagic, and still cast at will, but instead of having higher numbers of spells per day, they have the same number as the Wizard. And the Wizard actually comes out ahead, because they have an ability that lets them get a few spells back with every short rest! Also, they can prepare a fairly good number of spells, and cast them as needed with their spell slots, giving them greater versatility.
So the Wizard now has more spells per day and greater flexibility with casting. The Sorcerer gets metamagic. That's it, really. I think the Sorcerer either needs the same "regain some spell slots on a short rest" ability as the Wizard, or else needs more of their special sorcery points to make them more viable.
Still not sure about the Warlock (or the Bard, which is also now a 9-levels worth of spells arcane caster class). Maybe I'll analyze those two a bit more later.