Well, I put a piece of tinted lexan between the monitor and the hole in my Cocktail table, mostly because it hides the monitor. If you go with tinted glass/lexan on the top, the games will seem to "appear" out of the blackness....which looks good IMO. I had bought the glass untinted and realized this after the fact, so I did what I did to hide the monitor as much as possible. I'm happy with the results, but if I did it again I'd go with tinted glass for the top.
Some might not like the tinted glass b/c it does dim your display somewhat, but you can compensate by turning up the contrast/colors on your monitor.
Good luck.