This was alright. I honestly think these two books were a little too open-ended and vague at times, which might not have been the best for a group very new to the game (and a first-time DM).
I really just read it because I was curious if it was the DM making choices that made some things feel...off. Turns out no, it's just written awkwardly and the balance is deliberately brutal.
I also wanted to see what we could have done differently. In short: A lot. I think because of the brutality of it, it actually DIScouraged the party from being thorough. Particularly at the end, wanting to conserve our dwindling resources, we skipped at least 90% of the catacombs and just cut as quickly as we could to the caldera and Temple of Tiamat. In doing so, we missed the Draakhorn entirely.
Similarly, we killed the dude with the Mask, but in such a hectic battle in such an enormous arena where time is a factor and it takes several rounds to travel across it, we didn't spend any time at all once he was dead. As a result, Tiamat was not weakened by removing the mask from his corpse.
I do like the campaign concept and the idea of the episodes filling in a scoresheet tracking our relationships with various factions. I don't feel like that made any sort of difference in the end, unless I'm misreading the text, but it was a cool concept I plan to steal for future homebrew campaigns (although with much more explicit consequences and impacts, like being able to have the factions supporting you actually provide NPC allies or something rather than just giving you a pat on the back as you march to your inevitable demise).
I just think it could use a revision to tighten things up a bit. Leave an open decision tree, but perhaps provide a few more explicit cues along the way for the DM so the party can at least be nudged in the right direction (I guess the DM could do that themselves, but especially an inexperienced DM isn't going to deviate from the text). The perfect example is the Draakhorn at the end. There was no indication that there was anything to seek out in the catacombs other than a quick, covert entry to the caldera. Maybe if there was an explicit narration about how the party could hear the horn and it sounded like it was BEING BLOWN INSIDE THE COMPLEX that would be a clue to maybe take that out on the way in, given that it was such a big deal in the first episode but then never mentioned again when we didn't actually find it on the icebergs.
I feel like I want to run this (heavily modified) myself one day for another party, with those changes being aimed at better clarity and actually wanting to see the party have a fair chance at knowing how to set themselves up for success in the final battle.
I actually like that it presents failure as a likely outcome. That's ok! What's not ok is that, as a player, I don't feel like we knew how important preparation was beyond the usual training (leveling choices) and making sure we stocked up on potions and ammo. We had no idea we were potentially blowing past things we only had one chance at, like retrieving the Blue Dragon Mask at the tower (we did that, thankfully), or getting a nice arsenal of spell scrolls at the iceberg place.
There was no real hint that damaging the temple would disrupt the ritual; I even came within seconds of casting Earthquake to try to collapse a lava tube and cut off the reinforcements that were decimating us, which would have accidentally weakened Tiamat...nothing in the game, during or after the ritual, indicated that, it would have been pure happenstance.
Maybe you have some rogue bolt from the energies of the ritual ping a pillar and knock off a chunk of stone. The head cultist dude shouts angrily to watch it, they need to not damage the temple, and directs some underlings to scramble to quickly repair it with magic. Do something to actually give a hint to the players what will actually affect the ritual. Instead, we were left to guess, and our energies were entirely focused on just attacking wizards.
Fun fact: The arena at the end is just too damn big. Given the distances involved, unless your party has access to lots of spells like Dimension Door, or can deal massive damage at extreme range (even crossbows or longbows you basically need to position yourself directly below them to not be at disadvantage), it's simply too large. We spent most of the 10 rounds of the ritual traveling from one node to the next. We only ever came within one wizard kill of disrupting things as a result, and that was even making liberal use of our teleportation diamonds we found in Xonthal's Tower.
I think you do two or three things and this is an amazing campaign:
1) Shrink the final arena by about 1/3. Make it feasible to support one another and concentrate fire rather than having to split the party. This was the biggest issue, as our two healers (me (the cleric), and our paladin) ended up isolated and were focused down hard, utterly exhausting our healing before Tiamat even arrived.
2) Leave clearer guideposts. I'm not saying put the entire campaign on rails and remove the open-ended choices. Just make it more obvious which decisions matter and what will actually prevent the summoning in the end. Maybe have a captured cultist disclose details of the ritual, or one of the metallic dragons knows. Do SOMETHING so a party will know by better than trying things at random what will be most effective (e.g. the temple damaging example suggestion earlier).
3) Provide NPC guidance more than just the councils. Those were a bit vague and similar to #2 just didn't give a lot of guidance other than choosing what mission to go off on next. Have a knowledgeable scholar studying the cult in parallel who can update the party at each council even if they don't come along to offer suggestions. Decide in advance that one character's backstory includes intimate knowledge of the cult, or a history studying it academically. Don't just give the answers, but maybe use that as a fair avenue to feed hints as to what the party should be prioritizing to achieve the most good.
Overall I like the sense of urgency and doom here, I just don't think it's balanced correctly to achieve that while still offering better than maybe 5-10% odds of success. I think if you incorporate my suggestions, you don't diminish the brutality of the conflict. They just feel less helpless and can concentrate in the most effective direction available. This doesn't make it easier, it just keeps them from feeling ineffective.
I'd have felt so much better about dying to Tiamat had I at least known that I was fighting the good fight and doing the right thing, just coming up short, rather than finding out the hunch that was all I had to go on was wrong and a lot of our effort was useless. "I died because I just didn't fight perfectly" is a lot better than "I died because I was just flailing around and would never have guessed that damaging the temple or taking the mask off of the corpse's face would have significantly helped".