You guys are way too down on this guy, give him a chance at least. From the shift-by-shift game I've watched there's lots to like here although Kostenko IS a a later-round pick in a weaker draft so flaws are to be expected at this point and he most likely than not fails to make it in the NHL. That said, David St-Louis is over-analyzing here and belittling Kostenko's upside quite a bit.
Kostenko's first pass is pretty good, he holds the line well in the offensive zone both with his good agility and savvy little plays, owns a pretty nice array of shots, and he seems to be genuinely good at receiving even difficult passes while keeping control (now that is an underrated quality to have as a player). Then you also add the fact that he is actually pretty good at hitting people though I wish he cleared the front of the net with more alacrity, more proactively instead of only when opposing forwards activate and face the net with the puck.
As far as lacking hockey IQ defensively, I don't buy it. Kostenko's game lacks maturity, and is still really raw, true, but his decisions with/without the puck aren't ''bad'' per se, they just need quite a bit of refinement. I like his reads better right now than I ever did Broberg's, that's for sure.
One thing that might have influenced St-Louis' take on Kostenko is that the guy plays a more passive, ''wait and see'' type of game on D that we're not really used to in NA but can regularly be seen in Russia given the increased size of the rink and more deliberate pace of play offensively. To the unknowing beholder, that approach to defense might come across as him lacking drive or defensive IQ.
But look more closely and you begin to notice that his stick is generally in the good places out there, that Kostenko's pretty hard to beat 1-on-1, battles well along the boards, protects the puck pretty well along the boards/using the net to shield himseld from offensive pressure to pass the puck, and is just generally in good position out there to block shots/interfere with opposing forwards' sticks when it is important that he do so.
Again, not saying the guy is without flaws (will need to adjust his whole defensive game for NA ice, needs to be a bit less lackadaisical when holding the puck, start to pass more in the offensive zone instead of just shooting, improve acceleration/balance, etc.), or that he is even likely to be an NHLer, but we are being way too harsh on him despite not really knowing much about the guy, and we should wait and see how he progresses from now on.