Never even tried Hearthstone, I have a few friends who play it though. May have to look into it at some point.
Back to the topic of the deck.
This is honestly more of a preferential thing, but I personally have never really liked
Nullify. Outside of Mono-Blue decks.
Not just because of the somewhat restrictive casting cost (which is a hit against it, but not what kills it IMO).
Nah, I just generally don't like "creature" restricted counterspells. At least in terms of a deck that is looking to be more controlling.
In general control decks are going to have more than the average amount of methods of dealing with creatures already via removal/sweepers, and while it is nice to have the ability to counter some problem creatures with ETB/LTB stuff, most of these decks already run stuff like
Dissolve and
Traumatic Visions. Obviously
Nullify is a little faster, but how often does that make a difference? How many 2-3 mana creatures are there that are a significant threat that you need to counter, and other removal can't deal with just as easily?
My personal preference would be
-2 Voyage End
-3 Nullify
+1 Negate
+3 Shock
Shock deals with most of all the same stuff that
Nullify would early on, and while it isn't as good later on against the big bombs, it does add some reach to the concept of burning them out with Banefire/Obelisk, and you should have other removal/counters to deal with the fatties.
Negate helps to protect your bombs/Obelisk, waiting to drop Baneslayer or Inferno Titan or whatever other finisher until you have an extra 2 mana to back it up with Negate is often game over.
The last spot I am honestly not really sure about. You could make a case for a lot of different things. The second Obelisk being an option. As would a mise copy of some other removal spell (Reprisal, or possibly even Tribute to Hunger, since I see you already run Black for Obelisk). You could be really greedy like I am and try to jam
Resounding Thunder in there too lol.