Complaints I have seen of this game are that the accounting... is high
Yes Sentinels does have a lot of manipulation of Numbers, so does: Magic, Yu-Gi-Oh, WoW and any game where there is math behind it. It may not be as important as in sentinels, but they all have math behind it. Talk to theory-crafters trying to mini-max their lv 95 Frost Mage (is that right? I don't play WoW.)
Complaints I have seen of this game are that the ... fiddliness is high
Again, so is every other card game out there. What is the optimial play? Is there a better way of doing this? Do we win? If you want to play optimally, its fiddly like every other game. Try building that perfect Magic/Pokemon/etc... deck.
And the decks practically play themselves.
There is only a small number of decks which lend themselves to this. The only ones I can think of are: Tachyon and Haka. Tachyon naturally turns into a Dump your hand play style. Haka might discard cards or do some damage mitigation, otherwise he is straight forward.
Most of the Heroes have a lot of variability on playstyle, allowing the player to adapt to the situation.
Scholar can play as a damage soak with 3 Flesh to Irons or as a sustain Tank who whittles down foes with Solid to Liquid.
Wraith can be high damage (Razer Ord., Micro computer, Utility Belt and Throwing knives.) or High Utility (stun bolt, infrared eye-piece and utility belt.)
Fanatic can be damage mitigation (Chastise, Zealous Offense and Divine Sacrific), High Damage (Embolden, Sacrosanct Martyr and Absolution) or a hybrid
Tempest can be a LOT of things: Support (Reclaim from the Deep, Cleansing Down Poor and Shielding Winds), AoE Damage (Chain Lightning, Grevious Hail Storm and Electrical Storm), Single Target Damage (Lightning Bolt, Vicious Cyclone and Gene-Bound Shackles) or field control (Into the Stratosphere, Ball Lightning and Flash Flood.)
Mr. Fixer is damage which adapts to whatever situation he is faced with. He can become irreducible, gain damage, switch to AoE, etc...
My point is that most of the heroes have multiple play styles, which the players can use depending on situation and their preferred play style.