What are the differences in the difficulties?

Solution 1:

From personal experience, on harder levels:

• Monsters have more health
• Monsters do more damage
• I think they walk faster

However, also on harder difficulties:

• You gain more XP
• Monsters drop stronger and more valuable loot
• Monsters drop more mana

Solution 2:

According to the wiki, increasing the difficulty increases the rate of XP you earn and the quality of loot that drops.

Solution 3:

The only thing I've noticed on harder difficulties is that the monsters are more upgraded than lower difficulties. The monster upgrade symbol is above the monster and looks almost the same as the upgrade symbols for traps. These monsters have more health and do more damage.

Its also possible that on survival mode, certain monsters (like the super annoying one that heals other monsters), may show up earlier in some rounds though I'm not 100% sure on this part.