Never played mods, so, enjoying this.
Really, the improved terrain/cave generator algorithms alone is enough to make me fall in love with 1.8. I generated a new world, and it starts me on this island. A somewhat large island, with a lake in the middle. All I can see on any shore is ocean, save for the north shore and the south shore. To the north shore, I see a gigantic mountain jutting out from the sea. I eventually fashioned a boat and went over to check it out, and it turns out that's the mainland, I guess. The mountains are gorgeous. And that's where all the animals are. There are *NO* animals/meat on my island. I had to fish to survive, which was kind of fun.
I went back my home island, and eventually went over to the south shore. Off the south shore is a very tiny island. I figured nothing was there, it's barely big enough for a small log cabin. But I swim over and check it out anyway. Turns out that the center of the island is hollowed out, like a volcano, and under the island is a massive system of caves.
1.8 is full of things like this. I'm having more fun just discovering the world than I ever did in previous versions.