For anyone who has not read the Slayers novels 1-8, this post will contain spoilers, both for those and possibly either part of Revolution (depending on when you read this, relative to watching that)
Ok, the first thing that comes to mind is Zuuma:
-How is he going to recover his arms in Revolution, considering that in the novels he has to merge with Seigram to do it
-How come Amelia didn't get her "Zuuma!?" moment? Where it becomes apparent that she knows rather a lot about the very mysterious assasin, whom even Phil and Lina hadn't heard of. All things considered it makes sense really
Second are the relationships within the group:
Lina and Amelia: The number of occasions Amelia shows up in the nick of time to save Lina is staggering. I'd have to count but I think she does it more than Gourry. And Lina is obviously impressed by Amelia's skill as a preistess
Phil and Christopher: Don't think the anime could have been further off in that portrayal --or did they assign the role of Clawfell to Christopher, you think?
Gourry and Sylphiel: Considering the complaint Gourry made at the beginning about wishing there was a hot babe at the end of a run of banits and Lina's descriptions of Syl as being pretty much the epitome of grace and beauty, one has to wonder what exactly happened when they first met? I mean, Gourry remembers her -but beyond that she gets no attention from him whatsoever. And when Zel left the first time he asked Lina if maybe she was falling for him --jealousy much?
Amelia and Zel: Are SO a couple. Maybe not romanticaly (yet) but the number of times they speak for each other! "...at that point, Amelia and I may become your enemies" or "Mister Zelgadiss and I would prefer..." ---particuarly regarding their opinion of Xellos leaving nowkthx. And Zel just casually mentioning that Amelia taught him recovery "a while back".
Then there are observations on people themselves:
Lina - Does not fire off Dragon Slaves at the drop of a hat! Only a very select group of people seem to know her or have heard rumours of her for that matter, good or bad.
Gourry - Not great with names, but thats about it. No, he's not -brilliant- but he's hardly stupid!
Xellos - Stupidly powerful. An excellent villian, I've learned to hate him and love him for making me hate him, rather than love him for being the comedy villian. He ISN'T.
Amelia - just plain awesome. The first series of the anime does her no credit at all. Even NEXT doesn't really justify her fully --except that part against the red/gray balls.
Zel - not as prone to leaving the group as you would believe. When he gets dragged into an adventure he follows through.
Then there are just the weird things:
They ATE Hellmaster!?
"Nice like Gracia" Teeheeeheee oh, Lina...
Milgazia offers to kill Lina... okay, that might have downed the tone of the anime a bit but wow. They COULD at least have stretched to the Shabranigido theory.
Is Amelia a higher level preistess than Sylphiel? I mean... Ame was able to cast ressurection --on herself!
The Sword of Light was actually a demon!? I get it being 'of' Darkstar, --but actually OF Darkstar!? Was he fused with Volpheed at that point? Is that why it's a 'light' blade as well?
Did anyone ever find out what happened to Tarimu after Seigram was defeated? Daymia was already gone but...
At the moment, thats all I can think of ^^ sure there's more in there somewhere but -opinions people! =D