First, D&D is a role-playing game, id est a different kind of hobby. In fact, in a RPG you need only ONE rulebook; all the other stuff (sourcebooks, adventures modules, etc) are Optional!
That is because if you have enough imagination, you don't need all that stuff and play forever in any case, only thanks to your imaginative mind and the rulebook set (20-40 euros).
Techinically, I disagree completely on this point. Some RPG require only one manual, and then you can create whatever you want with your imagination. Some others can't be played with only one manual because the core rules are split over several handbooks (some examples: Rolemaster, three books, Character Law & Campaing Law, Arms Law & Claw Law, Spell Law - and honestly, if you play without the Companions, the game is really poor; Dungeons & Dragons old edition - 5 boxes, Basic, Expert, Companion, Master, Immortal rules; Advanced Dungeons & Dragons: at least three handbooks, Player's, Gamemaster's and Monsters Manual. Plus there are some games you need adventures written by others, like Call of Cthulhu: creating a Horror on the Orient Express adventure is kinda challenging). So, yeah, sorry pal, I can't take your point
Descent is a Boardgame: when you complete all the Quest the game is over. When you have challenged for hundreds of time the same 6 monster-types, you need new monster-types to challenge… etc
I'm not with you on this issue neither: Descent is rather an endless game, there are countless challenges you can face even wth the only core sets. And you have an editor to create your own maps and so on, and the monsters you can face are a little less than six. Plus, by adding expansions and so on, the game is *huge*.
Descent 2 stems from Descent 1, it's true, but it's also a brand new game, for many reasons. And in the core set you should have enough adventures to pay you back the price you paid for the new edition. Personally, I consider the two games as two different games (as I considered the first Descent a different game from Doom, even if they shared the same rules system), and I'm not interested at all (at the moment) in the conversion kit.
As for the price. Yeah, if you have all the expansions from the first edition you indeed have spent a lot of money, but still. How many hours of play? I personally have played 50 core Descent games, which means every game costed me 1.6 €, which is a perfectly reasonable price, for me. I have something like 30 other games planned before adding Altair of Despair, so the price / game will lower again.
Plus, FFG has released a new FAQ for Descent 1st ed, and they said another one will be published in the future, so that all the doubts related to the first edition will be solved. And honestly none forced them to do this, especially because the whole line is out of production. This means they will use Kevin's time to work on something they won't have any benefit for, and for me it's a sign a respect towards the customers.
Using all characters / monsters in the 2nd edition is something that can give a plusvalore to the new edition, the game will become richer, but it's not necessary in order to have the game working. So yeah, I don't have any problems with paying the kit (if I ever decide to get one)