If you're looking for a Japanese experience that is more pop-culture than traditional sightseeing, Round 1 is a good choice.
The first floor is full of UFO catchers, video arcade games, Puri Kura sticker-photo machines and other general family-friendly machines.There are more than 200 arcade games on this floor to choose from. Air-hockey, Mario cart, Haunted house, "Taiko no Tatsujin" drumming, dance games and many other skill, luck and coordination games pack the floor. You will find families, school kids, dating couples and groups of girls getting their puri-kura stickers made on this floor.
The Basement floor and 2nd floor is filled with more adult oriented games like gambling machines the likes of Las Vegas as well as video boat racing, horse racing and other games to collect tokens that can be cashed in at the end of a session. These floors are semi-restricted as children 16 and under cannot be there without supervision and once the sun sets or before it rises, children 16 and under cannot be on these floors at all. There are a fair few hobby gamblers on this floor who seem to take the electronic horse and boat races as seriously as the real thing.
The 3rd floor is the reception for the bowling lanes as well as the reception and rooms for Karaoke.
The bowling seems a little pricey, about 5,000 yen for 3 games for 3~4 people sharing a lane (no time limit), but the lanes are in good condition, you can get snacks delivered to your seat if you wish. The price includes shoe and ball rental (shoe sizes up to 28 cm). They have 52 bowling lanes. If you bowl as a family, the kids will get a complimentary UFO catcher game chance card to redeem on the 1st floor, we were also given cards for free tokens to use on the gambling floors. There is one bowling floor designated as non-smoking but it is often booked out, there is supposed to be limited smoking (or customers are to use smoking areas) until 6pm, but it doesn't seem very well segregated or ventilated- something to consider if you are sensitive to cigarette smoke. Alcohol can be ordered to the table and soft drinks are available from the machines on each floor. There are also toilets on every floor and a bowling pin costume you are welcome to try on and take pictures in whenever you like (ah Japan). The bowling is paused once an hour for a "lucky strike chance" when they dim the lights and anyone who gets a strike at that time gets a special prize.
Karaoke is quite a bargain here especially if you get a group discount. We tried a special price for a group of 10 people to sing as much as we liked for 3 hours for 10,000 yen (1,000 yen per person). This included the all-you-can-drink-bar and the facilities were very new and it was fun. It was hard to navigate the menu to choose songs, there was no English navigation option but if you ask the staff to show you how to list or search by song title, you can see some English songs you are likely to be familiar with. They have 30 karaoke rooms and some have special themes (One Piece, with drums, special lights, etc).
The upper floors offer 14 dart boards to play at, golf simulation and ping pong tables, and 8 billiard-pool tables. They also have three, coin operated baseball batting and pitching areas.
Open practically 24 hours a day (Monday to Thursday they only shut down between 6 and 10am), Round 1 is a great resource for people looking for a bit of mainstream fun or pop-sightseeing in Hiroshima city.