I played on Beta 1.5 for a very long time,I find the Beta is much more hard than current Minecraft because of the following reason.

Gameplay
-When you getting hurt,your health will not regenerate unless you eat
-Food cannot be stacked
-Cannot sprint or deal critical hit
-Armour is much weaker(include diamond)
-Some block took long time to mine
-Player and mob can trampling crop by walking on it.Making large farm is much harder to build.
-Fire burn much quicker and infinitely(removed in Beta 1.6)

Mobs
-Skeleton will strafing around you.
-Skeleton has faster firing rate but weaker damage
-There is a bug cause creeper explode after you killing a creeper while it hissing
-Creeper can see through wall like spider(only in some beta version)
-Ghast spawn very frequent in Nether
-Passive mob sometime will not drop their loot
-Passive mob can despawning when player is far away from it.It is impossible to start a farm in Beta.
-Sleeping in place without light can cause nightmare,skeleton will spawn next to player.
-A bug caused mob can spawn in more larger group in Beta 1.5
-Some player said mob sometime will spawn in your house.
-Slime is harder to find,making stick piston more harder to make.

World Generation
-No village,stronghold,mineshaft,etc.The only structure is dungeon.
-Chest can only generated in dungeon

Lighting
-When night time,it is completely dark.Mob is very hard to see from a distance
-Torch is much darker
-Torch will not flickering
-Redstone torch and lava's light is white
-Ghast is not affected by light,it is possible see it from far away even in dark place.

Combat
-No sword blocking
-No critical hit
-No charged bow,your bow is weak machine gun.
-No enchantment
-No item repair
-Every sword is slightly stronger than current version
-Fist can deal 1 heart damage to mob(Beta 1.5-Beta 1.8)

Mining
-Some ore took very long time to mine.Obsidian took 15 second,redstone took about 10 second.
-It is very hard to find a cave from surface
-Diamond and iron is much rare compared to current version.
-It is very hard to find a cave leading player to lava level.

Beta version Minecraft make me want to play Minecraft again(I was about to quit since I got bored of current version of Minecraft).It is more harder and more fun than current Minecraft.Just one thing which I hate about Beta,larger map size,when I create new world it used 1.5mb compared to current version 759kb.

Thanks for reading my blog.