Rather than being merely a member of the Vex Collective, you are now one of its Axis Minds. Your mental abilities have increased by an order of magnitude—improving the quality and quantity of your simulations and making you far more dangerous in combat. Optionally, you may choose to take the form of a larger, enhanced version of a standard Vex unit.
To go along with your new powers, you now have access to your own copy of the Nexus. While this nascent version of the Vex Network is largely empty, it does come with a token garrison of Vex units to serve as an initial force for you to command. Besides serving as a highly protected base of operations, this trans-dimensional, trans-temporal virtual environment allows you to access alternate timelines and manipulate your own subjective past in limited ways.
While it will take time to implement, you now have access to the most advanced forms of Vex technology such as the ontological weaponry pioneered within the Vault of Glass and the planet-sized simulation engines that power the Infinite Forest.