Suppression Cloak might be a nice support in general (although to be honest, there might be better solutions, such as better armor, or not getting hit in the first place), but the rest I find to be better suited as a "sideboard" (and I think every deck should devote a few points to sideboard spells) rather than the core of a a deck.
The problem with Suppression Orb and Mordok's Obelisk is that it presumes your opponent will be using a lot of creatures. Against a Beastmaster summoning lots of low-level creatures, it's fantastic. But against a deck with a few creatures or even a solo mage (or a mirror match), it's not as effective. Of the two, Suppression Orb is probably the least effective, because it's also not as useful against creatures with Ranged Attacks. And sometimes, battle becomes confined to one or two squares, so the mana-for-movement isn't so much of an issue.
And again, there is also the issue of recouping your investment in mana. These conjurations costs 8 mana, so if your opponent is only using one or two creatures, it'll take eight (or four) rounds before you recoup your investment.
Essence Drain is one of those Enchantments that needs to be carefully used. I mean it's terrific if you're fighting against a stupid player, but there's also a point where the smart move is for the opponent to simply not pay the upkeep cost and let it die. (Again, it depends on the target; Level 1 creature? I'll let it die. My level 5 creature? Sure, I'd pay it, although again, it takes three turns before you recoup your investment, and it doesn't solve the problem that the creature is still there, ready to attack you.)
In general, I don't like these cards because 1) it gives the power of choice to the opponent (i.e. they can choose not to pay it), and 2) it doesn't really solve the existing dilemma that your opponent has creatures/permanents that are a threat to you. Or in the worst-case scenario, you've built all this setup, while the enemy Mage themselves moves right next to you and start pounding you (Beastmasters and Warlocks deal more damage than you and have more life from the get-go).
Personally, 6 Nullifies are overkill for me. I usually pack two, although I can envision some people using 3-4 if they want to be particularly protective. I mean the smart move by the opponent would be to cast Decoy, Seeking Dispel, or simply summon creatures and conjurations to attack the opponent instead of casting spells on them. In general, I usually pack 2 cards of each that I find useful, while 4 of each card (or even 6) are the exception to the norm. (Cards like Dispel or Dissolve are probably a good exception--I pack 3.)
If you're looking for some kind of "control" deck, I'd probably recommend inflicting various status conditions on the opponent. Lightning effects tend to have a good chance of stunning, while the Basilisk can Cripple them, and the Gorgon Archer can Weaken them.