I have one just like it, but mine has problems with wax sticking to the sides. So, mine is not good but that doesn't mean they all are not. If it flows to your liking, if it is appealing for you to watch, it is a good lamp.
Welcome to OG Jamie.
These lamps frequently come up on ebay, I found one in charity shop but it went cloudy too.
Take a look here if you are after a good quality Lamp.... http://www.mathmos.com/
These were imported by Lyon Design, and were some of the earliest knockoff lava lamps to hit the US market. The first versions had a transparent colored plastic tip on the cap, which matched the lava color in clear liquid: blue, green, red, maybe purple. Then came these and Lyon's gas pump-shaped lamps. They had the same "only round globs" flow of most Chinese lamps, but additionally had a tendency for the wax to stick to the glass. Consider it an interesting lamp, especially if the lava still turns transparent when hot.