Nice! As far as staying true to the photo it looks extremely consistent. Only major differences I'm picking up are the nose and hair. The nose in your picture is a little less pointed, starting from the bridge. It might be worth seeing if the hair highlights could be diminished slightly so that it doesn't look so even over his whole body, but it looks great in any case.
Now am I mistaken or is this David Tennant?
Yep, it's David Tennant.It's a still from the movie he just wrapped filming on. It's a biopic about a Scottish psychiatrist from the 60s and 70s named R.D. Laing. He was a bit of a celebrity, and very controversial in his field.
I agree that there are some areas that aren't totally perfect. I'm probably going to leave it for now, just because I've already spent more than 20 hours on this painting, LOL! Plus I have some commission work coming up, so I need to finish before it's time to start that. I'm the sort of person who never goes back to a pic once they take a break from it, so I don't want to abandon it. LOL!