Few runs in Doctor Who history come as highly regarded as the Russel T. Davies and David Tennant era of the series. Despite most of their run being comprised of stellar episodes, the synergy between the showrunner and actor truly started to gel toward the end of their partnership. The latter half of the fourth series saw Tennant's incarnation of the Doctor grapple with crushing loneliness that set up four subsequent specials. If a Doctor Who fan was to argue that the season of specials produced by Davies and Tennant were the modern series' finest hour, it'd be hard to debate them.
In the video linked above, you can take a look at the teaser trailer for the Doctor Who 60th-anniversary special that reunites Tennant's Doctor and Davies. If Doctor Who has taught us anything, revisiting the past is almost always a blast, barring one doesn't run into an Ice Warrior or Auton.