Racial Bonuses are Larger
All Races (except Humans) receive +2 to one stat and another +1 to another stat (with one dwarf subrace getting a +2. This is in contrast to the final playtest where all races received either two separate stat boosts of +1 or a single stat boost of +2. The exceptions then being the Half-Orc receiving a +2 and a +1 and Humans again.
The Inspiration System
Only recently revealed in the WOTC Twitch Livestream, the mechanics of rewarding players with Inspiration for roleplaying their Flaws, Traits, Bonds & Ideals as a resource was new with Basic.
Personality and Background are suggested to be tied together
In Basic Flaws, Traits, Bonds & Ideals are tied to the background a player chooses for their character. These can either be rolled or selected.
The Biggest Changes are Optional Rules
Highlighted in light green at the end of their respective sections, some with the moniker "Variant." These choices were not foreshadowed or hinted at beyond vague mentions about 5e being a modular system. Expectations were that this modularity would not really show up till the PHB's release or later in the DMG. Doubtless larger options are to come, but these smaller ones were unexpected. Some examples: