Well, my edited last post kinda answers the question, I think. The Witchfire Trilogy has a great plot, it's a great setting, it's got a lot of unique elements (new monsters and threats, for instance, moral ambiguity -- one of the "main bad guys" in the earlier modules is an ally later on), great artwork you can scan and print off as player hand-outs, great cartography -- but it's very scripted, and is difficult to keep on track if you have groups that tend to not take the conventional bait you lay in front of them, or groups that come up with creative solutions to problems that the author's didn't plan for. Having played one of the modules, I found it frustrating that all our ideas were simply swatted down because the module didn't make any provision for them, and the DM didn't know what to do with our plans.
Freeport is another series that has great tone and theme, some Cthulhu-esque investigation, and even a crawl through the sewers that I think is neat. Both series are strong on plot, have great themes and tone, have lots of roleplaying opportunities (both being essentially urban adventures in many ways, and featuring lots of investigation and mystery solving.)
Reviews should be available here and at RPG.net for both series.