alright, I'm gonna list the ups and downs of 1.8 off the top of my head.
+Slime blocks (bouncy and sticky, how does that work?)
+New Commands (/clone is awesome on its own, but with everything else...)
+Armor Stands (Just look at all the fun stuff sethbling is doing!)
+Banners (Just awesome)
+New Block/Item data stuff (Being able to pick what can/cannot be broken with a pick in adventure mode? Genius.)
+Depth strider (I always hated boats)
+New doors and fences (Finally!)
-Ocean Temples (A pain to get in, and not worth the loot.)
-Rabbits (Cute, but bland, only slightly more useful then bats)
-Endermites (at least until the master plan happens)
-Andesite, diorite, and granite (at least make slabs and steps.)