Quite challenging to keep all the glyphs in mind. I played it two times and it seems the correct counterglphy does not change between sessions. So even if you know them beforehand, remembering the right one and reacting fast enough it no easy task (at least for me). Made it to a score of 48 the second time - just having three lives and six different glyphs to try for the last one makes death very likely. So either decrease the cool off or add some possibility to heal.
There are other possibilities to add to the game play. For example allow the player to knockout your opponents with glyphs yourself and add a level progression. Level 1 might be just one opponent that shoots always the same glyph, add more glyphs and opponents in successive levels. And you might even introduce some casting mechanics. Imagine you don't cast single glyphs but spells made from glyphs. So in later levels you might have an opponent prepare a spell consisting of three glyphs (that pop up over their head one at a time), and you have to remember the counterglyph for each one and cast a spell using these in the correct order.
Would be way too much for my memory, I guess, but others might deem the amount of challenge enjoyable.