If the lens is fully stopped down, as it might be for a sunny day and a fast film - say at f/16, then there isn't going to be much depth of field to talk about - most everything that's in the frame will be in focus. On the other hand, with the lens fully open, at maybe f/2 or f/2.8 there is going to be a lot of the frame out of focus. The faster the lens, the shallower the depth of field will be at full aperture. With luck your subject will be in focus (assuming that's what you want and that's not always the case - right?!) and the background out-of-focus.
Because different lenses behave differently, lots of photographer-type dudes and dudettes just love to try different lenses and see how they render those out-of-focus areas. In this post you can see some interesting bokeh in black and white. Here area couple of colour shots for your interest - both with shallow depth of field and a blurry backgrounds:
|Interesting background rendering|
What about this one?
|Cabbage white butterfly on thistle|
I'm not sure 'bokeh' can either be judged as 'good' or 'bad' - just different. Some might say if the background detracts too much from the subject - with either good bokeh or bad bokeh - then that's a Bad Thing. I think that the photograph is what it is - in the above snaps there is a definite subject (in focus) and a background (out-of-focus) and the viewer is aware of both elements of the photograph. If the photographer wanted, he/she could have cropped in real close to remove any background - so it's there for a reason.
I like the way different lenses render scenes differently, in a similar way to how different film/developer combinations behave. It all adds to the richness of photography.