All righty then guys, EnderCat here with a derpy new blog about...things that Minecraft should have. :P
Let's get started!

Small changes:

Mob heads should sometimes drop upon killing ALL mobs, not just Wither Skeletons.
Command blocks and mob spawners for all mobs should be in the creative inventory
You should have health bars displayed above your head.
There should be more structures, or at least make Villages generate in every biome, because it can be a pain in the butt to search for 3 hours for a stupid village and not find one
Villagers should have better trades that are actually worth something
More chests in villages, or more blacksmiths in villages
1 or 2 iron golems should spawn in a village when it is generated
Hoes should be more useful, like doing as much damage as a pick, in case of emergency
Chain armor should be craft-able with iron bars (not ingots, BARS)
Bricks should be throwable and do 2 damage
More stairs n' slabs! 
The ablility to place stairs and slabs sideways (like placing them on a wall)
When you place any two slabs (except stone slabs) it automatically creates a block of that type
Sliding glass doors, sliding doors, brick walls, barbed wire fences, fishtanks that give you fish if you right click them every 5 minutes, tables, chairs and couches that you can sit on, statues of certain players (yes this is in the Statues mod), marble, glass jars, dressers, curtains, TVs that show various youtuber's channels, radios, display cases that are like itemframes, quartz bricks, end stone bricks, mud (dirt that's near water), mud bricks (when mud is smelted), ender lamps (craft with ender pearls and glowstone dust), fridges, and pipes that transport water. (yes I know a lot of those are from various furniture and building mods, but I'd really like to have these in minecraft, it would make building more fun!)


Larger changes:

There should be more bosses, and more types of zombies.
I'd also like to see Giants be rare spawns and drop 16-32 rotten flesh, 4-8 carrots, 4-8 potatoes, and 4-8 iron ingots. They also summon regular zombies.
Wither skeletons should be as rare as endermen in the nether. (but still spawn in nether forts)
There should be more Easter Eggs in the game! (I love finding those)
There should be palm trees!
There should be crossbows, which are like regular bows, but require the use of logs instead of sticks, and have better range than normal bows.
There should be a Range enchantment for bows, that makes their arrows shoot farther.
Fire charges should be dropped by Ghasts and Blazes, and be throwable.
You should get Glass Shards when breaking glass or glass panes, and they can be crafted into Cracked Glass, which, when smelted, gives you Glass.
Sticks and Bones should do +1 attack damage, and blaze rods should do +3 attack damage and light enemies on fire, and also act as a flint and steel.
There should be throwable ninja stars (crafted with iron ingots in a circle shape) that do +5 attack damage on contact with enemies.
PvP combat should be more than just button mashing, it should require some skill
More ways to light up your world, because torches and glowstone don't really cut it
Being able to kick players and mobs, does 2 damage, or 4 if you are wearing any kind of boots except leather (press V to kick)
Large dogs like German shepherds n' stuff, also small dogs like Chihuahuas
Moving leaves and grass when Fancy Graphics is on
Berries!
More things to eat, like potato soup, and stew (put steak, pork, or chicken above mushroom stew in a crafting bench, gives you 5 chicken drumsticks)
Flowers that have smells (when you stand on the flower you recieve a potion effect)
Redstone Timer (makes redstone pulses twice a second, can be set to be slower)
WorldPainter and MCedit or something like WorldPainter and MCedit implemented in MC (builders like me would LOVE this!!)
Meat gets rotten over time and decays into rotten flesh, you can prevent decay by placing meat on ice, snow, or holding it in your hand in a cold biome.
Craft cobblestone into throwable rocks that do 2 damage when you hit someone with them
Snowballs have a chance to do 1 damage, and inflict Slowness on whatever mob/player is hit with them
Shelves that are crafted with 3 slabs of any type in a straigt line. For example, if you used quartz slabs, you would get a quartz shelf. If you used acacia wood, you would get an acacia wood shelf. You can place up to 2 items on 1 shelf, making it both a way to store items and a fancy item frame!
Cabinets that are similar to chests, and when they are opened they stay open and the items inside them can be viewed. You craft them with a shelf in the middle surrounded by planks of any type.
Stoves that smelt twice as fast as a furnace and have 5 different item slots for smelting. It requires both the same fuel as furnaces and a redstone block (no other redstone component) to power it. Craft them with iron ingots surrounding a furnace.
More types of fences and walls (this would be very helpful for builders like me)
Make the terrain more interesting, like having more variations in elevation (the world is more or less flat except in extreme hills and stuff) and having every forest be slightly different (like one forest has larger trees than another, or one forest has taller trees and more birch trees than normal) 
Craftable mob spawners (craft it with iron blocks around a skull/head of the mob you want it to be)

HUGE changes (not really related to Vanilla MC, maybe would be better as mods):

Robots!
This would include a:
Combat bot: Kills all hostile mobs, and picks up their loot. Kills stuff by shooting lasers at it.
Miner bot: A lot like the minions from the minions mod, they can dig mineshafts or stripmine, and they also pick up all the items they mine.
Transport bot: Right click to ride it, control with WASD, twice as fast as a sprinting player, and can swim through water and lava without being slowed down or being harmed. Also can act as a minecart that doesn't require powered rails and is faster. 
Woodchopper bot: Chops trees, picks up wood, saplings, and apples.
Armored sentry: Acts like a basic Combat Bot, but its laser attacks are 3x stronger, has 2x as much health, has a regeneration 1 effect, and follows the person who spawned it.
Suicide Drone: Runs at hostile mobs or players that have been hit by the player who spawned it, and blows up like a creeper, except it does not harm the player who spawned it, and its explosion is 5x as more powerful as normal TNT.
Evil BossBot: A robot boss with 500 health. Attacks you like a Armored Sentry, and kills both players and mobs. You spawn it like a iron golem, except instead of iron blocks it's a structure arranged like this:  
  H         H= robot head
RDR      R= redstone block 
  R         D= diamond block
Upon death all of these robots will drop 4-8 iron ingots, 4-8 redstone dust, and whatever is in their inventory. Their rare drops are robot heads, redstone blocks, and iron blocks.

There should also be a Kingdom RPG mode (which is a world type, in the same tab as Superflat, Large Biomes, etc.) where you choose a class (Warrior, Hunter, Archer, Mage, etc...) and you explore the land, hunting monsters, finding kingdoms with castles and villages (some kingdoms you are freindly with, some are evil) and you can do quests as well (e.g. Slay 50 Red Dwarves, Rescue the Princess, etc...) Also redstone ore does not generate (because there is no electricity in medieval times) and robots are disabled.
There should be Assasins that are VERY rare spawns, and can 1 hit kill you. They also have a lot of health, but have a chance of dropping a wither skeleton skull or a diamond sword. There regular drops are bones, and ender pearls.