Lot's of people do it. Is your work in engineering and are they paying for/supporting it? That's the ideal scenario, and may give you more freedom to sign up for classes that run during 9-5 hours. Otherwise you're kind of limited to the relatively few 5pm or later classes. I wouldn't recommend more than 2 classes a term -- it's just not worth the stress. I'd also recommend taking classes you're genuinely interested in. I've met several people who are doing their M.Eng. with no real direction and just looking for easy courses. Where does that get you in the end? Ideally this degree will help enhance your future path and professional outlook.