We have a bonus room over our garage, we have a 96 inch screen and a DLP projector up there, surround sound, theater seating and a snack bar. That definitely wouldn't work for your space, before we built the theater we had a ping pong table and all the children's Nintendos and computer etc.

Pool table maybe. How about a Pachinko machine? (an old japanese slot machine)
If I didn't need the space for anything else, I'd dress it up like an irish pub or maybe an old timey western saloon.

Real pinball machine, arcade size race car video game thing from the 80's, tv and video game systems, older table and 4 chairs for board games, refrig, ping pong table in the nearby storage room is brought out sometimes. My son is saving for an air hockey game. DH bought the arcade games as a reward for himself to celebrate 5 years of self employment (it was awhile ago.) 13 yo DS bought the ping pong table with some money he won. This is the family room in the walkout basement. The main floor family room just has a tv/stereo

Well, we don't watch TV or movies to any extent. We watch football & the news. So, we went another direction in our home. We've got a large bookcase with hundreds of books (some quite rare), a chess set, wood scrabble board, cards, a small stereo system, & my piano. There's a flat-panel 15" TV. I have the custom-made wingback chair of my dreams & DH has a leather chair & ottoman. The wood pieces are all early American antique with a lot of 17th & 18th century wine glasses & decanters sitting around (DH's collection). We also don't have children home any longer so the room is no longer "child-friendly". The grandkids love to sit on Grandpa's lap in that room & play "what's it?" pointing to the various collectibles. But, it's the only room in the house where they can't roam freely. lol

In years past, when the kids were still home, we've had ping-pong, tournament-size pool table, much larger stereos, larger TVs, darts, Whirlitzer juke box (really fun!), and a small dance floor. Have always had the books, chess, and one piano or another.

I love playing pinball. How about an electric dart board. You can go the gameroom route. The slot machine idea would definitely be great for guests.

Our room just has tables in it -- we literally use it only for games. My husband has a gaming night a few times a month, where we have about 8-15 people over to play boardgames. And cabinets to store all the boardgames, of course :)

I've always wanted to buy a pinball machine, but they're pretty expensive.

Our family isn't into foosball at all... we prefer pool or air hockey.
We are also BIG on board games.

Guess you should go with what YOU like!

When we moved into our house, I got to decorate all the upstairs and second floor, but the basement became my DH's lair. He put in a new subfloor and wall-to-wall in the family room area (there is also a laundry room and workbench). Because he is a golfer, he cut a hole in the subfloor and asked the carpet installer to make a corresponding hole in the carpet. Then DH got a cup and flag, and voila! instant practice putting green!

There is also a small wet bar with dorm-size fridge and microwave, a recliner and sofa, a 56" TV, a game table, and all his favorite golf and travel memorabilia. The Playstation2 is down there, so it's where my grown sons congregate when they visit!

I'm cordially invited to watch movies with DH, but it's really his space - he even does the vacuuming. :)