I think watching series 2 was harder without watching series 1. Rose was closed off at the beginning of 2 because of the regeneration and she grew close to the 9th. It's definitely worth watching, plus Eccleston's Doctor is awesome in general. If anything, watch at least The Empty Child and The Doctor Dances two parter. Definitely the best two episodes in the first series imo.
Yeah im very interested to see what they do with the XII doctor. They introduced him at the end of the season finale last saturday. I caught a little of the 9th doctor but couldnt get into him and the companion.
There are so many possibilities for who he is. I'm kind of in the boat that he's an older 8th Doctor that he has disassociated himself with for the atrocities that he committed to end the Time War, which would make sense with how the 9th was so closed off and angry. Plus it'd give us a chance to see a regeneration from 8 to 9 (even though Eccleston has firmly said he's not involved, Moffat always pulls twists out of nowhere).