Christopher Ecccleston has had his critics as the Doctor, but I think, in his role, he's combined wit and intellect, with humour and compassion. Billie Piper has been a bit of a revelation as Rose, and has proved she's more than just an adolescent boy's pin-up.
The Daleks, naturally, and the Slitheen have been the best monsters of the series. The special effects have mostly been good, and there's been a fine array of guest stars, including Simon Callow, Zoe Wannamaker, and Richard Wilson. Some of the stories could have been stronger, though. The World War Two two-parter didn't do it for me.
But, though it's gotten more cruder, with fart jokes and mild swearing, it looks like the series is in safe hands.