Adding more value - general upgrades as cards have got cheaper. Notably black has got better one drops ( Tormented Hero -> Cult Conscript, Gnarled Scarhide -> Bloodsoaked Champion), red's had a general improvement in power level and a push towards a better aggro deck. White's Elite Spellbinder and Giant Killer have gotten a lot cheaper, as has Vindicate and Will Kenrith, so they've come in. Finally, some of the (cheap) new hotness; both from Universes Beyond and other sets - e.g. Squee, Dubious Monarch, Rona's Vortex, Night Scythe etc. are all in as general improvements to cards.

Crystalline Giant has come out mostly for logistical reasons.