Sorry if you think this command sucks, but I have made Minecraft a little more like Terraria. Here are some things you can do: Summon the King Slime boss by throwing a Slime Block and Gold Ingot on the ground, make a Death Sickle by throwing a Stick and a Coal, summon Demon Eyes by throwing on the ground a Spider Eye and Glass Block, and even create a Trophy of King Slime by throwing 1 Slimeball and a Gold Nugget. Please don't tell me bad things about it, I just released it and will be adding more and more all the time.
Your map looks a bit empty with just a few buildings? Then you should check out this City Generator! Add this machine to your world by just using one command in only one command block! After that, you'll get a snowball, that you can throw and which will create large cities consisting of 10 slightly random skyscrapers! These houses have a modern look and blend perfectly into most town environments! (This is one of my older commands!)
I always have problems with creating large landscapes by hand. There is nothing more boring! In order to no longer having to do that, I have already made some structural generators. And this is one of them, this time for mountains and hills! Using some simple 'Only One Command Block' - magic you can easily create icebergs, dirt- and sandstone mountains! Besides that you can create some hills and smooth your environment as well! Another 'Fun Fact': Initially, this command was 40000 characters long. I had to shorten it to 32000 characters.
A re-creation of the Graves from OpenBlocks in Vanilla Minecraft - when you die, you will get a grave that contains all your dropped items. They will never despawn! Once you break your grave, you get the items back.