You can skip season 5, it's the definition of "tacked on".
The first half, maybe. But the second half is some of my favorite stuff from the whole show!
Definitely, although I think "Day of the Dead" is another one I like. It has its problems, however, it's written by Neil Gaiman, which imho makes it worth checking out.
"The Very Long Night of Londo Mollari" and "A View From the Gallery" are two other episodes which merit watching. Some good character moments, though nothing all that arc-related.
"It's not so much that it's 'shut down' as the government has been rebooted into safe mode."
- Tim and Daniel Shamblin