The amount of adjustments here are too numerous to list, but the main changes are the following:
Turret upgrades are no longer lone entities, but stack onto one of your two turret slots instead
Turrets now require gears for purchasing rather than coins
Gears are acquired by defending towers that spawn near a hero character once every minute.
Mobs now have more HP to account, requiring players to maximize their particular hero's upgrade routes in order to maintain character-specific DPS
Max HP scaling increased for all characters
Damage scaling increased for all mobs
Revives have been migrated from buyables to a 1 minute timer in game
The underlying code has been shifted from single player to peer-based multiplayer. Official, functional multiplayer is still in development, however.