Topic Glyph of fear
Irrelevant tbh. Glyph of Nightmares is the clear choice for PVP for example, amazing utility.
I feel like glyphs should still have three tiers:
1) Damage spells (Imp Swarm, Dark Soul, Soul Shards, etc)
2) Utility (Exhaustion, Soulstone, Fear, etc)
3) Vanity with no effects whatsoever on anything at all involving pvp or pve
Some classes really do need that 3 tier approach - Priests, in particular. That being said, it's hard to give more slots without giving everyone everything useful - i.e. eliminating choice.
Honestly, increasing the number of glyphs and glyph slots gives us more choice than giving us limited glyph slots.
Customization and personalization is choice, not having to sit down and think about DPS implications.
Glyph of Void (all demons replaced with Void creatures, Twilight creatures, Old God minions, and undead)
Glyph of the Fel (you already know)
Glyph of the Nathzerim (wtb Dreadlord meta form)
Glyph of Gender Equality (dat Incubus, and fem meta)
etc etc etc
Just add more glyphs and add another three or two glyph spots IMO