The game has multiple paths, multiple endings and a pretty robust new game+ mode (not only does everything carry over, but difficulty continues to scale up). Multiple playthroughs are required to experience everything.
Depending on how far in you are it might be worthwhile to finish your old playthrough (even if it requires a guide or something to get yourself back on track) and reach new game+ instead of restarting.
Real Civil Engineer (RCE) did a playthrough of the full game. What's great is watching him point out all the times when the game correctly or incorrectly flags safety violations, as well as commenting on all the things that a safe engineer would never do.