The PQ games are very procedural. There is challenge, but it's less about figuring out how to solve random puzzles and more about how to react to different scenarios and do things in the proper order. This series gave me some of my earliest gaming experiences, so I'll always have a spot for it in my heart.
PQ1 hasn't aged too well but it's a fun game - the VGA version is probably "better" in terms of playability but the original version and its parser make that one a little more fun. PQ2 is the best of the series and maybe best SCI-0 game Sierra did. Some people dislike PQ3 but I rather love it for the cult-oriented story. As the PC Gamer article says, PQ4 isn't a good game but it's still worth playing - you can somewhat appreciate what Gates was trying to do.
While billed as a 'tactical simulation', I gotta throw a little love to SWAT. That game got terrible reviews, but the missions were kind of fun to play. I also liked the branching nature of each scenario. The problem with SWAT was that it was too much of a tedious simulation or training exercise and not enough of an actual game. The FMV was limiting for the gameplay, but I still think what they did with it was kind of neat.
This site has some great reading on the series:
http://www.hardcoregaming101.net/policequest/policequest.htm