D&D 3E/3.5 What are the major differences between 5E and 3.5E?

[aramis erak]

Most casters combine prepared and spontaneous casting /and/ at-will cantrips, including marginally effective attack cantrips.

Marginally? You must have a near unique understanding of the term.

The attack cantrips are usually a better choice than a missile weapon for the magic user. In addition to being proficient in the spell as a default of the system and not being default proficient in most missile weapons (unless you're playing an Elf), and you do about as much damage, AND get to use what is likely to be your best stat (tho' it's possible to play a single-class sub-par member of any class).

And they're only slightly below the damage output of martial classes (Barbarian, Fighter, Paladin, Ranger) at low levels.

 

[Uchawi]

Casters that specialize do not lose access to general spells, they just become better at the chosen specialty. Martial classes do not require feat chains, but the ability to customize them are less based on being simple compared to casters and feats being more general and accessible by all characters with some ability requirements thrown in.