Some issues:

• Code blocks (prefix lines with a tab/tab width of spaces) looks like it matches too greedily. So, multiple lines of code blocks, which should be multiple code blocks, become a ton of recursive code blocks.
• Code spans (backtick) also don’t match right.
• Backslash escapes are not working.
• Code blocks in blockquotes aren’t recognized.

There are many more problems right now. These are the ones I can think of.