Season Five is pretty bad and betrays the quality of the show in a myrriad of ways. That said, if you loved the first four years, you owe it to yourself to see how it ends!
Unfortunately a lot of it was due to outside factors. JMS was told at the start of S4 that he would not be getting a fifth year so he condensed the series to wrap up in one year instead of two. Then when he got an eleventh hour reprieve at another network, he suddenly had an empty year to fill up. (I exaggerate for effect)
Then, he killed off Marcus thinking Ivanova would be in S5. Then in between seasons, a tragic negotation misunderstanding resulted in her being off the show. So he lost two of his best characters instead of one.
This resulted in the inclusion of a horribly uninteresting and poorly acted new character, and the bastardization of an already terrible storyline.
Then, at a hotel he accidently threw away his story notes for the first half of Season Five, resulting in even more subpar episodes than there might have been.
Then, his Season Five budget was slashed to be much lower, resulting in a near total lack of CGI space battles and action. Also, they lost a day of shooting, meaning that they couldn't do complicated action-y scenes anymore.