Warlock subclasses get benefits at 1st, 6th, 10th, and 14th level and they get an expanded spell list that includes two extra spells they have at each level 1-5 that other warlocks do not have the option to take.
Important note: This is from the tabletop game. Also the spells listed aren't automatically given. They're just options that a warlock would not normally have.
GOO get:
Features:
- 1st Level: Awakened Mind
- 6th Level: Entropic Ward
- 10th Level: Thought Shield
- 14th Level: Create Thrall
Spells
- 1st Level: Tasha's Hideous Laughter, Dissonant Whispers
- 2nd Level: Detect Thoughts, Phantasmal Forces
- 3rd Level: Sending, Clairvoyance
- 4th Level: Evard's Black Tentacles, Dominate Beast
- 5th Level: Dominate Person, Telekinesis
Fiends get:
Features
- 1st Level: Dark One's Blessing
- 6th Level: Dark One's Own Luck
- 10th Level: Fiendish Resilience
- 14th Level: Hurl through Hell
Spells
- 1st Level: Burning Hands, Command
- 2nd Level: Blindness/Deafness, Scorching Ray
- 3rd Level: Fireball, Stinking Cloud
- 4th Level: Wall of Fire, Fire Shield
- 5th Level: Hallow, Flame Strike
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A lot of GOO's spell list includes stuff that's often extremely useful on tabletop game but historically has been poorly implemented in a CRPG (In NWN Clairvoyance became +10 to Spot/Listen, for instance). Also, we're not seeing any stats for Awakened Mind which doesn't allow the ability to invade other minds so thoroughly as Detect Thoughts.
I don't have my books available at the moment otherwise I'd check.
My blog entry on warlock's is a bit out of date since it hasn't been updated for Tasha's, but it should be fine for BG3 barring differences between CRPG and TTRPG:
https://thrythlind.blogspot.com/2019/03/warlock-traits.html