My impressions after playing some of the cards and how they faired versus my expectations.
Overrated
Alesha, Who Smiles at Death: Body not as good as expected, ability sometimes lacks targets, ability conflicts with a lot of other themes. Decent card, but I doubt its a long term keeper.
Jeskai Sage: It might have enough play to it, but its slow. No one wants to kill it, but its not so much of a threat that anyone feels compelled to do so.
Mardu Strike Leader: The four mana mode never feels right. Maybe in a cube with asstons of sweepers its worth something. Ok three drop, feels better then
Ophiomancer.
Properly Rated
Yasova Dragonclaw: Aggressive stats, useful ability, but doesn't have much synergy and is somewhat deck restrictive. Pretty good card, not a lock for a slot
Warden of the First Tree: Its a one drop mana sink that can beat down. Better then a stupid 2/1. Probably has a long tenure.
Shaman of the Great Hunt: So swingy. Beats down hard, gives +1/+1 support, AND grinds card advantage? Easy to deal with, dies to almost anything. Very playable and interesting card.
Soulflayer: Best I got was Flying/Haste on turn 3. He's a mini tombstalker with a fun mini-game. Solid.
Goblin Heelcutter: It does exactly what it says it does and it does it well. Four mana mode feels wrong, but its fine.
Mardu Shadowspear: Its not great, but it works as a resuable extort trigger/champion trigger. I'm not sure I need the card, but its well costed for the role.
Under Rated
Shu Yun, the Silent Tempest: Absolute lock. Interesting ability and incentives unique choices. Explosive power level. Love it.
Citadel Siege: Two very different modes, both are good. Icy Manipulator is underrated. The Bolster mode gets nuts fast. Not essential, but being an enchantment is a huge perk. Solid Roleplayer.
Mardu Woe-Reaper: The upside on this is surprisingly nice. You don't always feel shitty topdecking this like most of its ilk.