Well, I think the title says it all. I know the definition of "lousy" is different for everyone, so I'm going to let you define it.

The supervisor-PhD student relationship is one of the most important factors in the success of a PhD. No doubt about it! However, passion for your subject and your project can take you a long way. As you hinted it also very much depends exactly what the issue with your supervisor is. As long as your supervisor is not obstructive and that you have access to the training you need from other sources, you can get also support on a day-to-day basis from others: fellow students, post docs, research assistants, research technicians, your second supervisor...

If the situation is really bad, it would be worth talking to your supervisor (do not call them lousy to their face!) or other people at your institution to find out how you can get support. Your last resort would be to start exploring the possibility of changing supervisor altogether.

The following article addresses some of the student-supervisor issues:

It seems like one of the main reasons for people dropping out or not completing.

Mine can be a slave driver at times but honestly, I like that. He's ambitious and expects his group to share his ambitions. It's one of the reasons I chose his group over my other offer. He's constantly asking how things are going, if I have any new results, suggesting things I could try out and it's great. Keeps me on my toes.

The worst supervisors seem to be the ones that take little or no interest in their student leaving them feeling isolated and lacking motivation. I've got a friend who started at the same time as me with a supervisor like that and he's achieved absolutely nothing in the nine months since we started. It's getting to the stage where the grad studies office is on both of their backs expecting an update on his progress every two weeks as they're so concerned. Said supervisor has been banned from having a student next year as well.