I just got all the chests, the game started good, but the string made it a lttle too easy to get food. I like it, when people are getting a little desperate, because of hunger. Struggling to make enough food at the start, I like cookies because they are a really poor food. Only marginally keeping you away from death, and you can't grow them...
The chests were too easy to get to, when the cobblestone generator was up and running. As I got all the chests in about 20 minutes. And when I got them, there was no more reason to play the game, as I had gotten everything...

Missing items...
-Grass block in first chest
-Could do with a task list, things to do that keep people coming back to try and get everything...
-Obsidian, the Nether adds weeks to a minecraft game. Along with tons of lava for making a gold farm, ores for making electrical gadgets, brewing stuff, etc... The Nether adds a need to get armour and potions...
-A 64 stack of Ender Sockets would be a good addition, for a hard to reach chest. You having to supply the eyes yourself, adding yet more things for people to do.
-Biome chests, each chest having a large biome area around it. Along with biome specific items and a stack of dirt in each of the further out chests.
-Maybe add other tree types as well.

Recommendations.
-Harder to reach chests, some high and some low. Maybe the signs on the chests giving clues, like co-ordinates.
-If its all chests, then maybe add 4 Villager spawn eggs to help you get more stuff. But the chest have to be tougher to get, you need to feel satisfaction at getting them. But don't put them all in one chest, as its soul destroying if you only get one chance and mess it up. Spread them around the chests...
-A lot more chests, that are going to challenge people to get. Going down is not easy in minecraft, have some up high above you as well...
-Maybe, random empty blocks. For mobs to spawn on and harass you as you travel, shaded blocks that allow mobs to attack during the day. A ring of blocks around your chests, like Saturns rings, to force you to only travel by day...
-Signs that mean something, co-ordinates to treasures, look up, look down.

There's loads more that you could do, to up the stakes and add more depth to the skyblock. As well as giving people the need for each item they get, as well as alternate ways to get all items and ores.

These are all just ideas, as I really love skyblock maps. I you like the ideas, then great. If you don't like them, then just ignore my post...

Hope you like my new map! :)