This is very well made! At first I was really confused on what to even do. First I shot all the letters, then I tried dodging them, and only after spending ages figuring out did I realise you have to stack the letters. My biggest advice would be to make it super obvious how to play because once you know what to do it becomes very fun. Very difficult, but still fun nonetheless. My high score is 21 which is pretty low but I'm proud of it.
Some minor things I also appreciated were how the letters change colour depending on whether they extend the word or not, and how cool it feels to bounce bullets on walls. Another minor criticism is that the voice clips are just way to loud relative to the rest of the audio imo.
I can't imagine how you even made this game lol, really good job. As a fellow british man I see the countdown reference so good job on the creativity there.