I pretty much agree with the 2 and 3 star reviews above. The only point I'll add is this - there are probably only 2 reasons to go to Mars at this location.
First, you've never been there before, and want to be able to say you have. The second is you haven't been for 25 years and want a quick hit of nostalgia. It pains me to say it, because I have fond memories of this place, but there are dozens of other diners in Toronto equal to or better than this one.