Apple employees downgrade Tim Cook

Yahoo (YHOO) employees love Marissa Mayer, but she hasn't been on the job long enough to be included in this year's list. Glassdoor requires that current CEOs receive at least 100 company reviews during the past year, plus at least 40 the prior year.

Mayer joined Yahoo in July 2012, rendering her ineligible. But she's doing pretty well so far, with an 88% approval rating based on 120 company reviews during her time as CEO.

You'd think that free iPhones and cafeteria food would have vaulted her to the top, but Mayer encountered controversy recently when she barred employees from working from home. Considering Mayer reportedly had a nursery for her baby constructed next to her office, the announcement struck some Yahoo employees as tone-deaf.

Still, Mayer's approval rating is far better than her predecessors. Scott Thompson gained just a 48% approval rating during his short tenure, while Carol Bartz fared slightly better with 54%. Jerry Yang, who was also a Yahoo co-founder, received a 43% rating.

NEXT: Michael Dell gets big boost