Need to spice things up in skyrim!!?

You may enjoy playing as the "classic" warrior of your race. For example a Nord will only wear Iron armour, join stormcloaks, fight with sword/shield or Khajeet sneaks lots, steals stuff, avoids people generally, high on Skooma...

Take on a role- be a paladin who only does the noble decision, a theif who steals for a living- screwed if you caught doing so, assassin who only sneaks...

If you want to go for the Assassin Build you are talking about any race would do but the best would be Khajeet. To make it more difficult you may wish to only wear leather but you could use any light armor. Perk the Sneak and onehand skill heavily. Have 2 good daggers upgraded as high as possible (you want to dispatch targets ASAP. Join Dark Brotherhood early, use Theif or shadow standing stone.

Any Race will do:
Set the game’s difficulty to Hard. And or,
[*] Play your warrior Dragonborn, without using any magic (except were absolutely necessary). No Enchanting. Can only use found/stolen/bought items of magic. May use Health potions, but not make any potions.
[*] Play as a Mage. Cannot use any armour. Can only use daggers.
[*] Play as a thief/assassin, May only wear Leather armour, may only use dagger, short sword, and bow. No shield, no magic, the same as the warrior.
[*] Play as a Paladin. May not do anything unethical, cruel, or illegal.
[*] Play as a Cleric: Any armour is ok, may only use Rally and Healing spells, weapon is either the Mace or Hammer.
These challenges should make for an interesting game.
One other thing you might do: If the Dragonborn dies, start over.

Orgies.