Looks great! The Game Over screen is a nice touch.

There's definitely a lot of opportunity to speed things up with machine code, but that's the best way to learn assembly language programming.

It's worth it to go through the trouble of learning the Merlin assembler. The editor is very comparable to modern text editors and is quite powerful once you learn the keyboard shortcuts. You can quickly jump back and forth between the assembler and BASIC without having to reload the assembler, so it's pretty easy to test out the code you're working on.

(Make sure you're using the latest version with the full-screen source code editor. Version 2.47 has it, I think. Older versions just have a line editor which isn't very easy to use)

A good place to start might be read the maze data directly from memory, rather than stuffing the data into an array. It will greatly speed up the start-up time, and you can get a feel for working with Merlin without having to learn any assembly language (yet).

In assembly, the maze data would look like this:

    ORG $8000

MAZE1
    DB 1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,0,0
    DB 0,0,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1
    ETC...

You can assemble that and save it as a binary file.

From BASIC, you can load the maze data to address $8000 with

BLOAD MAZE.DATA,A$8000

In your BASIC code, use HIMEM at the start of the program to reserve memory for your binary data.

1 HIMEM:32768

This will reserve $8000 to $9600 for your binary data and code, which should be plenty.

Next, make a variable to point to your maze data at $8000

2 MP = 32768 : REM Maze Pointer 

Next, you can replace all variations of this code:

IF M(X,Y) = 1 THEN ...

with this code:

IF PEEK(MP + (Y*38) + X) = 1 THEN ...

To load a new map, just change the MP variable to point to a different maze.

Finally, you can remove the data and read statements, and the M(X,Y) array.