We already saw that. http://www.startrek.com/page/star-trek-deep-space-nine
The way the characters and the plot developed together was great. Some of the episodes were uncharacteristically dark for the Star Trek universe (introduction of Dukat's daughter, Garak and Odo, etc.)
In TNG, the only credible existential threat was the Borg, and you really only felt that for a couple of back-to-back episodes. The Borg were awesome, but DS9 had greater sustained dramatic tension.
And the camp episodes! When DS9 did silly, they did it up right--with frickin' evil mirror universe characters and tribbles!
It's very good.
It takes a little while to get going, but the story is probably one of the finest arcs on TV.
Also don't forget star trek: voyager, my personal favorite.
Was a fairly descent wrap up if you're looking for some closure.
> a series like TNG will never be made again
I have higher hopes than ever actually. With Netflix creating their own TV shows, crowdfunding booming, as well as cheap alternative movie and CGI studios popping up worldwide, we might some day see something even better than TNG.
Edit: I mean, look at Stargate Universe, that how had incredible potential, and fit pretty much with the above "new economy / new audience" description.
I wouldn't be surprised that once the equity crowdfunding JOBS act passes properly, we'll see independent Netflix style TV series be funded, at higher per-episode funding than current TV.