I haven't run any of them (though I wouldn't mind running 'Sunless Citadel'), but my impression after reading through all of them but 'Sunless Citadel' was that they weren't particularly good and probably followed the usual TSR trend of making the suggested levels too low for the challenges involved. For a long term campaign, for most groups, the difficulty does not have to be tournament level. One has to remember that in the old days, the minimum suggested level of a module was often based on the assumption of 8-12 players, and even now, my suspicion is that the minimum suggested level of the adventure path modules is only going to playable for 6-8 characters in most cases with a reasonable tough and experienced DM.
I think one of the biggest problems with published modules is that even in the case of some of the best ideas the author doesn't have the space to tell you how he himself would run the story and much of the detail is left out. This means that there really isn't anything like 'run it as is'. I generally find I need one pages of notes for every 4 pages of published module before I feel comfortable running it, so in general I expect it to take a week to work up a regular sized published module for play. Expect to do that work, and be prepared to add a story to what is usually just a disconnected series of encounters. In particular, most published modules are woefully lacking in NPC's to have dialogue with.
If I'm running a whole series of modules I generally expect to link them to together with a bit of wilderness adventuring and semi-random encounters (meaning random encounters that have had the details fleshed out before starting the session). I very the length and number of these 'side-treks' depending on how many levels I need the party to gain. In particular, with the published modules you list the question is not whether the previous module can take the party to the minimum suggested level, but whether it can take a party to the middle of the range of suggested levels. I don't think that taking the party to the minimum level is a good goal for a long term campaign, as it is likely to result in a higher than desirable turnover in characters for even experienced players.
Drawing upon my personal experience as a DM, I wanted to follow the then adventure path of B1, X1. But B1 was woefully short on story, which forced me to completely rework the map so that a more linear progression would naturally occur, as well as introduce a few NPC's and flesh out other ones to give the PC's some knowledge of what they are involved in and a sence of purpose. Since X1 was to follow, it was reasonable to fill in the details of the temple with icons that pointed towards X1's final encounter. These weren't just random evil guys, these were would be servants of those that held the black pearl of power that would be the goal of the next adventure, and naturally they also had the map of how to get there. The adventures were then linked by a voyage to a seaport. Along the way the party killed a pair of ogre bandits that had been terrorizing a small farming community, fought off assasins of the evil cult, got in a barroom brawl with some orcs, and dealt with a pick pocket. In thier quest to hire a boat to take them to the isle of dread I introduced some NPC's I planned to make use of later. Once on the isle of dread I fleshed out a voodoo cult among the natives and added so forth.
So, basically what I'm saying is that while published modules can be alot of help, don't expect them to do your job as DM for you.
