Does grease burn? if it's anything like bacon grease, it's basically turning the Area of Effect into one big candle with the target as the wick?

At one time yes. I'm not sure that still applies in the new ruleset.

grease

https://www.dndbeyond.com/posts/513-spell-spotlight-grease

Shouldn't this give advantage on escaping grapples as well?

Good spell for

• holding off bottle necked areas
• making a getaway
• attacking a surrounded large creature
• making people slip in font of large crowds 
• Setting up an ambush: aggro monster, turn the proverbial corner spell caster casts grease, melee attackers now potentially have advantage on attacks on ambush target.

unfortunately not a keeper in most cases. probably good to have on the side and prep if you know that you are likely to be in one of the above situations.

Begs the question, if I can cast any spell a spell with the point of affect literally on a creature - why can't I cover monsters in grease?
I'd personally tweak the spell so that it covers creatures in the area of effect as well as the ground with the option of either rolling a save at the end of each turn or using an action or remove the grease.. more useful that way.

Unfortunately, not very good. To be effective it would need to upcastable. Increasing area of effect and then applying an increase to damage if the grease is set on fire. As a 10 foot area it is garbage, many creatures can just jump over it. Its only saving grace is its effectiveness against heavily armored targets. But casting a spell to deal 0 damage and knock a target prone is just okay.

best spell in the book

Pair with spells like booming blade or create bonfire from another caster to maximize the punishments; damned if you move, damned if you don't.

Grease is fantastic because it doesn’t need concentration- you could cast create bonfire yourself even

Yep! 🔼

Have another party member cast a fire spell on the enemies caught in the grease, and watch as the flames engulf them!

How would you rule fire damage from a grease spell lit on fire? Would the damage change based on what the source of ignition was (ex. would an upcasted create bonfire-lit grease do more damage?)

The casting materials are items that don't really burn well or very fast, so unfortunately while the area might be very slippery the pork grease or butter would not be nearly as instantly flammable as something like vodka or gasoline. If you hit it with a spell strong enough to light the whole area on fire, the initial spell would do more damage by far than the flames from the grease, although they would continue to burn for a longer period than the initial spell.

Would this cause creatures to slide drown a ramp?

Available for Sorcerers as wel due to Tasha!

So basically a 10 foot cube, that most enemys could just jump over, that gives you a chance to halve someones movement? 

What a waste of a Level 1 Spell-Slot...

I'd use it on the heart of an opponent. Instant clogged arteries, causing heart attack