Drinking this regal-appearing essence of pure power sets you on the path to becoming a true ruler and exemplar of humanity, with all the limitless potential the Emperor of Mankind held before his tragic fate.
*You are now a Perpetual, a variant branch of Humanity that possesses true immortality. As the mightiest of the Perpetuals your extraordinarily rapid and efficient cellular regeneration is capable of almost immediately healing any injury up to and including your complete disintegration. This regeneration even persists after your clinical death, allowing you to self-resurrect after being killed. Only true soul-death is capable of actually ending you permanently, although sufficiently ludicrous physical overkill can delay your resurrection for a time. And you of course possess an infinitely long lifespan, an absolute immunity to things such as diseases and toxins, the ability to survive for incredibly long periods of time without sustenance of any kind, maintaining perfect physical readiness without effort, and similar little tricks.
*Your soul is also exalted and magnified, starting out with the collective strength and power of all the psykers of ancient humanity and only growing from there. You have the potential for every psyker ability known, hinted, or even vaguely implied for the Emperor of Mankind or any lesser psyker in the lore of 40k and a full understanding of your powers and perfect control over them. With time and practice you may develop even more advanced applications of your psyker abilities or learn how to wield them with optimal tactical efficiency.
*Your mental and physical abilities are likewise perfected and exalted, removing all prior infirmities or derangements and making you supremely talented at any field of endeavor that you could possibly know or do. Even with barely any training or experience at all you could still easily match even peak humans in specialties that they had trained obsessively at for their entire lives, and should you devote actual effort to self-improvement then you could rapidly progress from there, Likewise, your strength, speed, resilience, intellect, perceptiveness, and other such attributes start out already well into the superhuman range and may also be improved.
*Your body is likewise altered in a manner befitting your new and glorious state of existence. You become a perfected human in all physical aspects. Your 'default' form is that of a human being (if an exceptionally attractive and impossibly fit human being), not an eight-foot-tall demigod-construct, but it would be a trivial feat for you to use your biokinetic talents to reshape you into that form or any number of other humanoid forms either temporarily or permanently.
*Your mind and soul are adapted to handle eternity as well as your body. Your memory is perfect, with infinite storage, perfect indexing, instant recall, protection from tampering or harmful memories, and other such features. You are fully acclimated to a perpetual existence, leaving you with your full capacity to feel and act according to your sense of ethics while still being able to accept things such as the passage of time, the inevitability of outliving mortal friends and acquaintances, and the weight of ages without excessive regret or pain. Time will not dull your edge, inactivity will not cause you to degrade, and entropy alone will never bring you down.
*Your willpower and resistance to corruption are absolute, limitless, and unbreakable. No amount of distress, suffering, or difficulty can make you hesitate for the slightest instant. No physical, mental or spiritual taint can touch you, however subtle or terrible. No force in existence can beguile or subvert your mind by any means whatsoever, not even memetically. Should the Ruinous Powers themselves all assail you in concert with their worst tortures for an eternity of eternities, you would not so much as blink. This indomitable sense of self does not make you incapable of admitting error or maintaining rational habits of thought; it merely means that nothing will ever dictate your choices save your own free will. You may conceivably be killed, as nigh-impossibly difficult a feat that would be, but you can never be broken.
*Should you happen to enter the Warhammer setting your powers and nature would interact with the Warp in the same way that the Emperor's does, including his ability to help create other psykers. In any other cosmology your powers are independent of the Warp which almost certainly doesn't exist there anyway, and it may or may not be possible for you to foster and unlock psyker potential in others depending on local conditions.
*Most wondrously of all, your ultimate potential knows no limits. You will never reach a point where you cannot grow any further, never hit a plateau beyond which you cannot improve, never be doomed to physical, mental, or spiritual stagnation. The only limits upon your growth are those that you knowingly choose to place on yourself and the ultimate limits that apply to any sentient being in the particular cosmology you inhabit.