Interesting topic. I'll go over my thoughts point-by-point.

It's a bit unfair in some ways to criticize Divinity 2 - the resources required to create a world like Divinity 1 are a lot less than what you would need to do something similar in Divinity 2.


Game world
In terms of the game world, Divine Divinity definitely is better. There are clear zones of different areas, deep forest, farmlands, towns an cities, battlefields, and desert. In Divinity 2 there's one farm in Broken Valley, maybe one or two in High Hall, and I really don't know where all the people live. There was also

But more importantly, in this world which is noted for having 6 main races (actually more), you can encounter areas where each of them is dominant. In Divinity 2, there are Humans, Goblins and a handful of Imps. The diversity is gone, and the other 4 races other than imps get maybe one mention each at most. It makes the world feel smaller and more generic.


Combat/Gameplay
Divinity 2 gets the edge in combat. The kinetic fast-paced movement and fluid animations are a pleasure to play and watch. The skills are a bit more balanced, although the offensive magic line could have used more diversity (only 4 spells?).



Rewards
Divinity 2 gets the edge here, but not by a lot. There are more unique items to be found from exploring, and they're more useful. The ability to choose your own quest rewards is also better. Divinity 1 gave free points in specific skills, Divinity 2 gives you skill points you can use on whatever you want.


Freedom
Due to the smaller game world, Divinity 2 has less freedom. On the other hand, a lot of Divinity 1's freedom wasn't helpful - you get no direction at all on many quests and have to guess.

Divinity 2 is about even on freedom to build your character. You don't get as many stat points to play with, but you do get many more skill points.

Divinity 2's dialogue options are much better than Divinity 1 - you can make a paragon of virtue, or a giggling psychopath, and you can express that in almost every conversation. Divinity 1 didn't give you that much freedom, you generally were stuck in white knight mode if you wanted to actually do quests.


Story

The quality of the story is about even, but I would give the edge to Divinity 2, because its more tightly focused. There’s no main plot in Divinity 1 until after you finish the first dungeon, and it takes an extremely long time (Stormfist Treasure Room) to even figure out what’s going on.


Humor

Both games have moments of humor, but the edge goes to Divinity 2 again. The main character gets a lot more opportunities to be snarky, and there’s more humor in general.