When it's working you can take a lorry, car or bike across (50p I think) but at the moment it's out of service due to corrosion found on some of the rivets holding it all together.
I live about 5 miles from it - I can see from my window - and have been across many times but still enjoy the trip and often go out of my way to use the bridge.
As Bob says well worth a visit. But closed at the moment. When it reopens try to arrange your visit on a weekend or Bank Holiday when the Upper Walkway is opened, take the bike across and leave at the other side, come back on the Gondola and then go back via Walkway and take a camera.