Depends on what you want to do. When I saw the ad for GGTS' PhD program I remember thinking, "Oh yeah, they've got a PhD program." and being surprised.
GG is a nice seminary that makes up for the lack of robust faculty with a stunning campus. They're a decent school but seem to never get beyond a certain circle of influence. Maybe its the west coast thing, but you'd think given their location and proximity to such a wealth of significant ministries they'd grow like crazy.
They do have some excellent faculty, but the place is stifled. That's one of the reasons I was so glad that San Fran was able to host the ETS/SBL meetings this year. Maybe some more exposure to GG.
All that said, it's not the best PhD if you want to teach. Here's the thing, and this is what I say to a lot of people, PhDs are
flooding the market right now. Even more than before and humanities PhDs specifically are out there like crazy. This is fine but the problem is most schools where you might teach aren't expanding their humanities programs. Even more so when it comes to a religion or divinity track. So what do you want to do with it?
If you want to pastor or have the ability to be a missionary who has academic credibility to teach in a 2nd or 3rd world school than its a fine degree. (Honestly I see PhDs taking over DMins in about fifteen years anyways...that is PhD being the preferred degree for pastors) But if you want to teach in a stateside or European school it won't get you far in the process. If you want to do the latter point go to a major school, do a MA/PhD there and rejoice when you're done. Then apply to schools.
Not being snarky or belittling GGTS. Like I said its a nice seminary. But why would they hire a guy with a DMin as their President if they were a major school? Think small, miss small imho. (I like their President, he's a nice guy but I'm just sayin)
The field isn't as open for academics right now and the guys who have been, or are, academics aren't retiring en masse anytime soon.
So why do you want to do the degree?