You have to bear in mind that there's a large gap between this current run of the series starting with Christoper Eccleston and the previous one which ended in 1989. There was a TV movie in 1996 with Paul McGann as the Doctor and then nothing until 2005.
The program started in 1963, so, as you can imagine, a lot of the old series are going to seem very dated by today's standards. But if you can get to watch them, you may enjoy them. A lot of episodes were lost over the years because the BBC didn't archive them, or they taped over them.
I think it's fair to say that all the Doctors have had their good points and bad points. I said at the start that I liked the Colin Baker episodes - but I didn't much care for them at the time as he played the Doctor very differently from Peter Davison. He had a huge ego, was completely crazy and he treated his assistant (Peri) like dirt. It's kind of funny to watch it now.