There is a moment in Maiev's hero spotlight where she is specifically described as powerful against high mobility targets. The video then shows her killing Genji after he attempts to escape. 

Very fitting for the current climate in Heroes of the Storm.

Players have been fed up with extreme mobility Heroes for some time now, and the recent surge of Genji and Hanzo picks during the HGC has only exasperated this feeling. If there has ever been a time for the ultimate bounty hunter, jailor, and otherwise "you-aren't-getting-away-from-me" avatar of justice to join the nexus, it is now.

Maiev has a varied pool of abilities that, when compared with her older Warcraft 3 peers such as Muradin, show the extents of how much more complex new heroes are as compared to older ones. Almost all of Maiev's abilities require a certain situation or specific requirement to be meant to be the most effective.

Fan of Knives asks players to hit groups of enemy heroes, less suffer a long cooldown.

Umbral Bind asks players to strike groups of enemy heroes in order to get tether all of them to Maiev's location, similar to The Butcher's lamb to the slaughter.

Spirit of Vengeance is a blink ability, but must first be thrown out like a projectile. The player then decides when to blink, or perhaps to not blink at all. Similar to Tyrael's El'Druin's Might ability.

The cherry on top is her trait: Vault of the Wardens. It causes her to leap into the air, becoming invulnerable for the duration. This means that skilled players will prove extremely slippery when playing as Maiev.

My first impression is that Maiev continues the trend of Melee Assassin's become the hardest and most complicated heroes to play. Valeera, Zeratul, and now Maiev all require precise ability usage and novice players will find themselves dying over, and over again.

Will Maiev really be the counter to the highly mobile Shimada brothers that currently rest at the top tiers? Her lack of single target damage is a little suspect, but Heroes of the Storm has always been a game about CC and Maiev has a lot of it.

Shoutouts to the Warcraft 3 Shadow Strike ability as a level 20 storm talent. It's just not a warden without that iconic sound.