I've run my group through the series. We skipped Deep Horizons(#6), and we're partway through Bastion of Broken Souls (#8).
I like the series. It's a large, complex, multi-layered story that really deserves some mapping of relationships between modules (if you're going to run all/most of the modules), and attention to the small details that link some of the modules. #6 is the only module that, as presented, has no tie-ins at all to the overall story (and as such, I skipped it, choosing to insert my own adventure at that point).
It's a bit of a monster farm, taking you on a grand tour of the MM, plus some custom monsters, and some parts are heavier combat than others, but on the whole it's good.
Some caveats, however.
This series was not built with the splatbooks in mind. It doesn't take into account things like the possiblity of everyone in the party having Boots of Striding and Springing (the PCs can always afford better toys than the NPCs, given the larger budget). If you have intelligent players, the module may break (or at least strain) at places if you're running it as written. Modules have some inconsistancies (most recent one I found was Lord of the Iron Fortress and a monster apparently too big to leave a certain room, which makes me wonder how it got there to begin with....)
This series is wonderful for the fighter types, the skill-monkeys, and the casters. Your ranger and druid will probably start getting cranky due to the fact that there's lots of dungeon and not much outdoors (though they do get opportunities to shine), and the last two modules involve planehopping.
I do not feel that this is a series fully appropriate for a novice GM unless that GM has lots and lots of time and understanding players (both of which I had in spades over the last two years I've been running this), but it IS good for a novice group of PCs.
Would I run the series again with a new group? Eh. Not likely. I'm finding, as I run my second group, that I much prefer smaller vingettes and running multiple mini-modules/adventures per level, rather than commiting the group to a single module for 1-3 levels. (I say this with some irony as that group moves towards beginning Return to the Temple of Elemental Evil.
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