Replaying the first level(s) is kinda repetitive due to always starting with the same units therefore just using the same strategy over and over again because at this point the enemies pose no challenge. To solve this you could possibly add some randomness to your starter deck (let bobs brain be a random unit for example), or as alternative you could add some different enemies that force using a different strategy early on (although this might not be preferable due to information-overloading new players). One last possibility might be some sort of 'challenge/reward', where before the level the player can take on a challenge (e.g. only use 18 spaces). If succesfull they get a reward (e.g. coins or an item) and if they fail maybe some sort of penalty. This would at least force some kind of variation on the first couple levels.
The game has a great concept, I'm looking forward to see how it'll progress!