I'm pretty sure this idea was suggested a long time ago, and, I think it would be a great idea.
I think that, approach-wise, a GB TV Series could really contrast to the GB films the way the Highlander TV Series contrasts to the (first) Highlander film. Namely, the big budget FX and action-scenes would be toned way down for TV, and they could make it into much more of a character-driven dramady/action/sci-fi show, with particular emphasis on the drama (like the Legion miniseries started to do). Of course they could always do the occasional “comedy” episode, or other “genre” episode (like X-Files, Buffy, RGB, Highlander, etc., etc.) which would be cool I think. I'd love to see a full episode, just once, with no ghostbusting or anything - just some of the guys on their day off or whatever - just for deviation purposes. Maybe even a day-in-the-life of Janine episode.
And unlike RGB, I think they should stray away from the ghost-of-the-week concept. Generally, I'd like to see more build-up with the more serious ghostbusting cases, and on a regular basis I'd prefer the ghostbusting to take more of a B-plot, with character based A-plots.
They could however also learn a lot from RGB. I would love to see a live-action version of Laura Summer's Janine, and in general, a more RGB look to the actors themselves (minus the crazy blonde Egon hair, and probably minus the multi-colored flightsuits).
One last thing I think would be amazing about a GB TV Series, is, as someone alluded to, the opportunity for CSI-type spinoffs. Ghostbusters of course belongs to the ‘occupational’ sub(sub?)genre, and its singularity results from the unique fictional concept of ghostbusting; it's not so much about the specific characters, as long as you have some Ghostbusters, and proton packs, traps, ectomobiles, etc., it can bear the franchise name: “Ghostbusters.” And you wouldn't even necessarily need spinoffs; from episode to episode you could follow the NY GB's, then the Chicago GB's, then the LA GB's, etc., and they could mingle and meet with eachother from time to time. That would ensure that the audience never gets bored with characters or locations. As long as the stories are interesting, and the FX stay affordable, a series like this could concievably last for a long, long time.