Brother Corbulo is Sanguinary High Priest to the Blood Angels. He holds the duties of a codex chapter's Master of the Apothecarion and shares certain duties with a Reclusiarch as he keeps many of the chapter's relics, though the Blood Angels do have their own chaplains. Of all the relics he keeps none are more treasured than the Red Grail that was used to catch the blood of Sanguinius after he was slain aboard the Vengeful Spirit and still it contains his blood after ten thousand years. Somehow. This chalice is used in the creation of all Blood Angels' recruits as drinking the blood of Sanguinius is the final step in the transformation into a marine (though this makes one wonder why the flying fuck Corbulo keeps carrying the thing into battle). Of all the Blood Angels Corbulo supposedly the truest of his father's sons, though not purely in the physical sense. He is said to have his father's deep wisdom and even his gift of foresight, a talent that has served his brothers well. Corbulo foresaw the second war for Armageddon long before it happened so the Blood Angels were some of the earliest to answer the world's call for help. Also notably an actual scientist in the traditional sense. Unlike the Mechanicum or the typical Apothecarium of your typical chapter, Corbulo and his subordinates actually use logic and experimentation to solve the gene-curse of the Blood Angels and their brother chapters, though this doesn't always work out the best for them.
On the Tabletop
In game Corbulo is a more expensive Sanguinary Priest with a few extra goodies. He has ATSKNF, Furious Charge, Independent Character, and his foresight is represented by allowing you to once per game re-roll a single dice (yours' or your opponent's) of the following types: To hit, to wound, scatter, saving throw, reserve roll, or seize the initiative. His warlord trait is Speed of the Primarch which adds 1 to his initiative, As far as gear goes he comes out of the tin with power armor, a Bolt pistol, frag and krak grenades, a narthecium, Heaven's Teeth (a Str+1 rending chainsword) and The Red Grail, a relic blood chalice that adds +1 WS and I to any blood angel within 6" of Corbulo (including himself; this bonus is not included in his above profile).
As far as actual tabletop worth, Corbulo is.. Impractical at best. For sixty points above a Sanguinary Priest you're getting +1 initiative, +1 (rending) strength and attacks in melee. Alternatively you could spend the exact same number of points to get two Sanguinary Priests, or get one priest and a minsquad of Tac Marines or Scouts. Sure, one to one he's objectively better than a Sanguinary Priest if you ignore points, but he isn't point efficient enough to justify taking him. Unless you're running a really fluffy list, don't bother.
Whilst it is true that you could take 2 Sanguinary Priests for his cost, and given how scarce they are in the current edition due to their being moved to HQ and it would be perfectly legit to want as many as possible, Corbulo can arguably be point efficient if used correctly. When paired with a Terminator Assault Squad, he is downright horrifying. Firstly, he himself is actually WS6 and I6 due to the effects of the Red Grail, and on the charge he is initiative 8 (yes, EIGHT!!!!!????) if you make him your warlord and S6 Rending, plus a 3+ and 5+++, which is absolute madness at 120 points, and that's only him. If you pair him with Terminator Assault Squad in the 3xTH/SS configuration, you now have a squad where in addition to the stuff they already have, the ones with Lightning Claws are I6, all are WS5 and they have a 5+++ in addition to their already ridiculous saves. Oh and also there's that re-roll he gives you, which can be used at any time for any roll provided he's still alive. Basically when used properly Corbulo is an excellent HQ in his own right and a brutal force multiplier. Finally, if his points value really bothers you, just compare him to Captain Tycho who is 10 points more.... see what I mean? Use Corbulo well and he's great.