Is this a good mill deck? If not, what should I change?
4 Belltower Sphinx
2 Circu, Dimir Lobotomist
1 Dimir Doppelganger
1 Mortivore
4 Reef Pirates
1 Szadek, Lord of Secrets
4 Vedalken Entrancer
1 Copy Enchantment
2 Followed Footsteps
1 Leyline of the Void
1 Glimpse the Unthinkable
2 Psychic Drain
1 Echo Chamber
1 Millstone
1 Mizzium Transreliquat
2 Paradise Mantle
1 Tower of Murmurs
8 Island
8 Swamp
4 Duskmantle, House of Shadow
2 Izzet Boilerworks
1 Urza's Mine
1 Urza's Power Plant
1 Urza's Tower
3 Howling Mine
1 Helm of Obedience
1 Thought Dissector
Sideboard:
2 Reminisce
1 Demon's Horn
2 Kraken's Eye
1 Bamboozle
3 Feldon's Cane
2 Grinding Station
1 Mesmeric Orb
1 Tormod's Crypt
1 Voltaic Key
1 Whetstone
It seems you have a number of subpar mill cards, like Reef Pirates. You don't have the really heavy hitters, like Traumatize/Haunted Echoes. In general, the deck looks a bit slow and I think most decks would roll over your defense. When using Howling Mines, you need to be able to mitigate their effect on your opponent with something like Arcane Laboratory or Mana Breach. If you are using howling mine just to mill your opponent's, there are better cards than that, like Mind Funeral, or 4xGlimpse the Unthinkable.
Propaganda works well in this sort of deck, especially if you have a few decent blockers for the creatures they can pay for.
If you want to get tricky, you could do a combo like Sunder + Jace's Archivist + Pendrell Mists.
If I recall correctly, successful mill decks are usually very control heavy, with things like Wrath of God and Damnation.