A couple years after I left my former employer, I received a bonus for the work that I had performed. The employer issued me a 1099 misc. Should I have received a w-2 instead? Please advise. Thank you.

Form W-2 is for employees. If you were not an employee when the bonus was paid, 1099-MISC is the correct form.

Yes, normally employers should send W2. But some employers do send 1099-misc.
How you will treat the 1099-Misc income, read: Your U.S. Tax Return: W2 vs 1099-Misc: Employee vs Independent Contractor.