The cable car is definitely a must-do when you are in Wellington, because it offers such great views of the city, takes you to another part of the city you might not see otherwise, and is cheap! A return ticket is $3.60, or $2 if you have a student ID card. I personally thought, when I got to the top, that I should have bought a one-way ticket (half of the prices listed above), because you can always wander down through the Botanic Gardens, although it is a bit of a longer walk to the city than otherwise.
The cable car itself really fascinated me. Its terminus is behind the shops on Lambton Quay--there is a signposted walkway that takes you back into the station area, which is essentially a ticket office and a small platform, and rails leading at quite a slope up the hill. It makes sense that the cable car is designed the way it is--rather than being level, but at the same time making everyone sit at a slope for the duration of the trip, the inside is staggered, so to walk through the car is like walking up a flight of stairs. I haven't been on many cable cars, but I certainly haven't been on any like that!
There were a few stops on the way up, but I didn't really mind as the views were getting increasingly better all the time. I also got a glimpse of the university area that my friend was studying abroad in for the semester. At the top, there was a nice little shop and mini-museum that housed a few of the previous designs of the cable car, which included one where people sat on benches on the outside! I can imagine that would have been an interesting ride.
I then went to the main attraction of the cable car--the viewing platform. This offered absolutely amazing views of all of Wellington and the harbour. It was pretty cool to go up there after having been in Wellington for a few days, so I could actually pick out places I had been (including some pretty obvious ones, like the huge Te Papa sitting on the edge of the water). I really felt like I could see most of the city, clustered around the water. The harbour itself was nice to look at as well, and I seriously considered staying up there to watch the sun set, but I didn't have the motivation to sit up there for a couple hours after having wandered through the Botanic Gardens.
As I said before, this is a great way to see the entire city, takes a relatively short amount of time (the cable car couldn't have taken more than 5 or 10 minutes to get to the top), and is extremely cheap, so why not ride the cable car?