I've done 5x5 and the progress is fine for a while--for strength--but after I while I just used it as in-season maintenance for sports. There's nothing wrong with it but at some point I feel there are hugely diminishing returns that you won't see so soon with more varied approaches.
If you look at some of the recent topics, I asked about new approaches to str/power and some solid programs were listed. Pretty much all of them beat 5x5 for long-term str.
What are your goals? Check out westside, texas method (some of the same ppl behind it as ss' 5x5), juggernaut, 5/3/1 and really anything that gets into strength science and programming.
Science and Practice of Strength Training by Zatiorsky & Kraemer is a great source b/c a lot of nuanced training programs seem to be mostly derived from it. I have the 2nd edition but if there are newer editions I imagine they'd be better.