I haven't seen a single episode. Is it any good?
I think Doctor Who is pretty good overall. It's a kind of a hit-or-miss thing. Some episodes are simply amazing, other episodes are boring or just plain weird. For me it went like this:
Christopher Eccleston: First Doctor I've seen. It starts with him if you start with the 2005 reboot series. It was difficult to warm up to him, but near the end of the season I really liked him. I was sad he already had to go after 1 season.
David Tennant: The reverse of what I felt for Eccleston. I loved Tennant right away, but near the end of his carreer as the Doctor I started to grow tired of him. He's an amazing actor, but his character development was inconsistent as f*ck.
Matt Smith: Absolutely loved this guy from start to finish. the second half of season 7 is terribly boring though, but the finale of Matt Smith is amazing.
Peter Capaldi: We've seen only 3 episodes of him so far. The first episodes was weird, but the other 2 episodes where amazing. I really love Capaldi as the new Doctor so far and I think he has the potential to become my new favorite Doctor.