While I wrote some of the dialogue, Gaider also wrote dialogue for characters he didn't write in ToB.
I think the appeal of Ascension is that it fits into the existing game, does so in a way that appeals to the majority of players. Yes, enemies coming back from the dead is cliche, but cliches hang around for a reason, they work, people like them. In this instance, the cliche makes sense. On top of it all, this was the end to a major serious that people had invested months in... having all those old enemies come together for one last time, for most people that's EXACTLY what they wanted, and THAT is, IMO, why people like it so much. It gives a sense of closure that was missing originally. Some well known faces come along to bolster the "came from nowhere" Melissan (and Dave used to always spell it Mellisan
)
Tactics doesn't do so well because it puts in hard fights here and there, but Ascension puts in a tough fight where you'd expect it: at the end of the game. Not only is it tough, but it's epic. You have spells blasting everything, demons being summoned, items being used... it all comes together in this one fight. There's also the fight that each member of the five is well known now, and you see their personalities coming through in the way they fight, each being defeated in a different way.
It's hard to explain, but I can see why Ascension is so popular. Yes, I'm sure the Dave Gaider name doesn't hurt, but I think it's more the area it chose to modify more than anything that won it its place. The ending was weak, people wanted something harder, something... epic. Ascension is there to give them that, and I think it did pretty well.