In time, which adventures do you consider the high points of the AP? And which are the low points?
Of the adventures I've run so far, Siege of Bordrin's Watch is by far the best. A couple of really fun fights in there (though I changed the stairway fight a bit to make it so the fall wasn't insta-death) and the pacing worked fairly well.
The worst for me, was Umbraforge. The adventure makes a lot of assumptions as to what the PCs will do, and as a result, comes off as very railroady. I ended up keeping most of the encounters but reworking much of the "story" of it in order to give the players choices and to avoid some of the blatant railroading.
Others that I've read, but have yet to get to, that look good include: Temple Between, Mottled Tower, and Haven of the Bitter Glass. I'm still reading through Alliance at Nefelus, so can't really comment after that.
I do have to disagree a bit with the earlier sentiment that the arcs are not connected, etc. I can't speak for the Epic Tier since I have not gotten that far yet. However, the heroic and paragon tier arcs while clearly separate arcs in and of themselves are also related. Essentially, the main villain of the Heroic Tier is basically the "advance man" of the main paragon tier enemy. Now of course, I don't know if this continues or not through Epic, but knowing the general story of Epic tier, there again seems to be some connection.
I will admit though, that if you want to really tie it together, there will be some work required on your part, but as I suggested above, I actually think that's a good thing since every group has different motivations. In contrast the above poster who mentioned the Necromancer, my group could care less about the names of the assorted merchants. So even though, Rufus can be made into an excellent NPC, he's nearly useless for my game in terms of story, etc. On the other hand, Captain Aerun and Bram Ironfell are getting substantial play in my group as I've introduced both of them early and both are now handing out missions to the group (necessitated in part by two near-tpks).
I think the biggest potential problem in tying everything together is that the path assumes that there are no tpks and that at the very least there's some original PC throughout. Even that though is fairly easy to counter act. The path is not perfect to be certain, but I think it is definitely very useable, particularly if you are a bit cramped for time. Unfortunately, I cannot comment on War of the Burning Sky as I have not read any of it.