The Decision Trees add an interesting "dynamic" in that they provide a way of "tracking" the modifiers with an area on the card that allows the players to use a "Dry Erase Maker". And from that point forwards, you can easily use the "Calculator" to play with a card's STATS (+/-).
The "Calculator" was designed for this purpose. It allows you to choose two opponents to "face-off" against each other and then allow "modifying" the stats if the card/unit has been given some "modifiers". Of course, the outcome is "hard" to predict and maybe some rules should exist (like the defending player uses his/her modifiers FIRST and then the attacking player gets the opportunity to use his/her modifiers LAST).
As I mentioned in another comment, the "good" thing about "modifiers" is that they ENHANCE a card's stats. Which means a card WITH "modifiers" is ALWAYS "stronger" (when attacking or defending) than the original card/unit alone. That's very important because there would be confusion: should I use my "modifiers" or not?!
Therefore "modifiers" are trackable, enhance (when attacking AND defending) a card/unit and are generally compatible with the purpose of the "Calculator".
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The tile laying mechanic is what drives the "composition" of the Keep. You must place a card next to (N, S, E, W) another card. The game starts with a "Nexus" card which allows players to choose where they want to place their FIRST card. In 2 Player duels the Keep is 5 x 5 (in size). In 4 Multi-Player games the Keep is 7 x 7 (in size).
Area control mechanic is very similar to "Tic-Tac-Toe" in that you wouldn't want to give a victory to an opponent by playing the wrong position. MK has something similar in that card vie for spots in the play area. But OTHER spots are "controlled" by one or more opposing cards. That's the Area control: some spaces are left open until the very end and you hope that you can FORCE a player to make a "bad choice" towards the end of the game.
Lastly I mentioned Attack Patterns. Each card has specific WAYS it can attack (or take an opposing card/unit). Like in Chess, a card maybe under attack by one or MORE opposing cards. That's when the "Calculator" becomes useful in determining which card would benefit more from the Conquest of the opposing card. But you just can't attack whatever card you like... You need to obey the Attack Pattern and sometimes this means that a card needs to be between you and your target.
That's a bit more explanatory (and verbose).