Finally got to give Minecraft 1.8 a whirl (had to download a new .exe so I could log in and update). The new lighting engine is lovely, and the outside world looks gorgeous at night. I also like the new bow mechanics and the food bar is a nice addition (recharges your health if full). And food FINALLY stacks in the inventory. Also, little touches like chests opening when you look in them are nice.
Since I'm still playing in my old world, I'll have to travel to another map if I want to see some of the bigger environmental changes. I don't know if it was just bad luck, but I noticed that underground creepers seem to spawn more aggressively. I rounded a corner a few times last night in an area I thought was secure from mob spawning only to have a creeper blow up in my face.