I closed mine in. I had 5 windows that were 50's vintage, ground level, tilt in windows. They had large openings with 1/8th" glass panes. The metal frames were rather heavy but they ill fitting/sealing. More or less they were unbelievably inefficient (may as well just had 5 huge holes in the house) and were very unsecure.
I caulked the frames shut. I literally filled in every gap around all 5. I also heavily caulked the windows in as a lot of the glazing was crap. I had 1/4" metal plate cut to fit the frames on the outside. Ground out the old paint and a little rust then I welded the plates over the windows. Primed and painted to match the house. On the inside they were already framed into the wall. I put in some 2x2 strips to give me some space off the window to account for the arm that was used to open them then I insulated that space with some unfaced bat. For the 3 actually in the game room (1 is in the bathroom) I used the 2x2 as a stop for some plywood backs I cut. Screw into place, fill the holes, caulk the perimeter to take up any irregularities...and bingo. No more leaky cruddy broken 60 year old windows and no more easy access to the basement for some unscrupulous individual. The side effect is a nice in set shelf.
Some may ask about safety in terms of getting out in an emergency. No problem. First off to the right of the pic, about 6 feet away, is the 5 steps to get out the back door. To the left of the pic, about 4 feet, is a double door large enough you can drive a car through that leads to the drive way.
