HR, employees and managers all have a love/hate relationship with performance appraisals.  Regardless of which camp your emotions lie in, the appraisal process is intended to be an honest discussion between the manager and the employee about the employee's performance.  

To ensure managers assess employee performance over the entire appraisal period versus recent developments (Recency Bias) only, I always encourage managers to maintain a file on each employee.  The file is to contain documentation outlining the employee's highs and lows throughout the year.  S/he receives a kudo from a team member or customer, a note goes to the file.  If the employee requires assistance on a project, a note to file for potential training.  This process also has a secondary value.  It requires the manager to take time to know his/her employee.  

Communication is key.