By consuming the essence of the Alicorn, you gain several boons:
*You now have the ability to transform into an alicorn pony from My Little Pony: Friendship is Magic. You have no issues getting used to your new alternate form, and know how to cast every spell ever shown in the show, movies, comics, or any official side content. You start out as strong (and as tall) as Princess Celestia. Your magic is like a muscle, allowing you to increase its strength with training and testing the limits of your spellcasting capacity.
*You get to pick your special talent, which will be reflected in your cutie mark. You will naturally be better at any activity involving your talent in some way.
*You have the ability to permanently transform mundane equines into their sapient counterparts as they are depicted on the show through direct physical contact. In the case of races that obviously don't have real-world counterparts such as unicorns, hippogriffs, pegasi, bat ponies, and so on, then you can still make them from bog-standard horses. However should you be in a world where they DO exist, you will find that they will be of a higher 'quality' if you choose to transform them, compared to those made from normal horses. You can also make sea ponies, mermares, and sirens from sea horses. Hope you have a really big pool in that case, though. Those you transform will be absolutely loyal to you, and regard you as royalty.
*You can decide a pony's special talent as you're transforming them, or you can leave it completely up to random chance. But for straightforwardly powerful' talents - like for example Twilight Sparkle's affinity for all magic - it takes a proportionate amount of energy to create a pony with that talent. This means that if you wanted to create a unicorn on par with Twilight, you would need a LOT more energy than you would use to create a fairly average unicorn like say Rarity.
*You can create other alicorns, but those take even more energy than freakishly powerful unicorns. While still absolutely loyal to you, they regard you as a beloved parent or older sibling rather than them being another loyal subject. The other ponies you make will also similarly regard them as royalty.
*Those you transform will also have the ability to assume human' forms. So they generally won't be able to pass as actually human unless you're in a world where rainbow-colored skin is normal. But hey, you can try to pass it off as a freaky skin condition? Maybe it'll work?