I was never able to find Wages of SiN on the net, so I couldn't play it.
The series wasn't picked up because SiN, even though it was an excellent game, didn't sell particularly well. In the rush to beat Half Life to the market, it did have some serious technical problems (not all of them were solved either, like the occational random CTD). I have heard that even on a 500 MHz P3 (the best of the best at the time), the loading times were very long.
SiN did beat Half Life onto the market, but that didn't garentee its success. I have played both games and I think that SiN is more interesting.
I personally didn't play SiN until just a couple of weeks ago. Even then I didn't buy it (because I hate steam and the CD version was impossible to find). I do remember playing it at a friends house all those years ago, but I couldn't play it because my machine was obsolete (166 MHz Pentium, compared with my friends 300 MHz P2).