i think first of all i would change the sprites of plants to somehow reflect their abilities to instantly remove the burden of remembering the ability-plant pairings from new players' minds. Also, i would like some visuals for the different abilities other thsn the score popup. And if i can present a more radical idea: i would add sort of side quests like: have 4 cucumbers placed next to each other. And have the revard be that they are then cleared from the map. I think this would balance the randomness and it would also add some short therm goals to keep the players engaged.
Let me know what you think of the ideas