Assuming the card gallery is accurate to what we will get in game (roughly a 50-50 chance at this point), here are my initial thoughts on stuff. Based on my Ixalan posts, I’m probably wrong (will review after a month or so of playing), but here goes.
Kicker: This is a simple and elegant solution to kicker. Only issue I can see is how it ruins cascades (since your second card won’t have enough mana to be cast anymore. Still, I like it.
Legendary/Historic: Making Legendary an evergreen and nothing else is fine. Sometimes the simplest solution is the best one. Historic is exactly the same as in paper, and historic triggers seem to be added to even more cards than in paper, making it more relevant. Looks good to me.
More Support Types: Fixes a big hole from the past in terms of differentiating. Also allows for semi-targeted removal, since you can specify a type (or not a type). Still not a perfect system, but going in the right direction.
Unique Tokens: Since I can’t see what the tokens are I can only assume they are the same as paper. I like the idea of unique tokens to prevent weird stacking (most obviously Josu adding to an already large stack of zombies), but its annoying that those creatures essentially take up 2 slots. Definitely limits usability.
Legendary Sorceries: Look powerful and fun. Some look better than others, but thats nothing new. Lets hope they work right.
Saprolings: I like how they changed “sacrifice” to “remove a reinforcement” to make it more usable with the token theme. Not sure why they had to make Slimefoot even more powerful than he already was, but hey, op uncommons are good for everyone.
Wizards: Look super annoying, just like in paper! Nice job. Wizard’s Lightning should probably do more damage, though.
Mana Bonuses: A nice unique way of doing “gain mana” effects without repeating the usual convert gems thing. Also makes them less overpowered and loopy, since you don’t get tons of extra matches every turn. Also, it takes game strategy in a new direction. Thumbs up to this (even if it makes green a bit less powerful)
Yargle: Still best card ever made. You cannot change my mind on this. Kudos for changing nothing from paper.