Very hard starting out, easier once you get the hang of it, good jam entry! I concur, it's a neat concept, there's a really fun game to be found here. I would consider the following: increase the slime pick box size, make it easier with fewer and slower slimes in the start, don't make "slower slimes" a progression as you typically want to feel _more_ powerful as the game progresses, make (it clearer that) longer chains brings in more points, especially the difference between 2 and 4 should be substantial.
Great entry, worth iterating on!