DC is playing catch-up when it comes to its film universe, hastily assembling the Justice League after the success of The Avengers and the disappointment of Man of Steel. Only time will tell whether or not they can successfully pull off this vast interconnected landscape, but if they want some advice, then they don't even need to look as far as their biggest rival. They just need to look at their own TV shows.
When The CW launched Arrow back in 2012, it was an unlikely home for a superhero show, and people questioned whether they could make it work, or even if there was any interest in a character not wholly taken seriously. Fast-forward to 2016, and the network has launched its third DC-based show, itself a spin-off (in part) from another spin-off, The Flash. Added to that, they've also brought Supergirl into the fold from CBS.
All four shows have shared characters, crossover, and unquestionably take place within the same universe. It's the sort of thing comic book fans love to see, and it's so far working incredibly well. Gotham may stand alone, but it's another example of how DC is succeeding on the TV side of things, making a Batman show without Batman actually work. All of these shows have their differences, regardless of the universe, but they're all undoubtedly comic book shows. 5 series, one big comic book world; unsurprisingly, there are an awful lot of references and Easter eggs to spot.