I'm just going go through these point by point, hopefully that makes it easier on you CarThief for forming a reply instead of me just making a huge post with many points in them

Hmm... Well, being basically a one-man team doesnt make large scale changes such as map conversion any easier (though i'll note the 32 start position for later fixing), but i'm trying.
For making the changes, I could do it in about a minute or so per map. I'd say at most it takes 40 minutes for a complete conversion of all the maps to UDMF and ensuring that all the start points are there.
Those mentioned scenarios about balance are currently quite map dependant, and rehauling all the maps is a gigantic pain and effort to do in one go, i mean, even Cutman back in the day didnt do much about the maps, its hard to make them more balanced yet still as the author atleast visually intended the map to be, even harder if the map is complex and has little to no space for improvements or widening, such as GVH11.
Making the map balanced would be really hard, the nice thing about GVH:NS is it brings to the table balance in a different sort of way. If the icefiend or any ghoul can camp in a certain spot and kill with 95%+ guarantee, I'd say it's poor map design and unrelated to us (or something we should fix).
I certainly wouldnt mind seeing more addon-friendly ACS myself but you'll have to make some suggestions on what you exactly want, as for me it isnt too hard to make entirely new scripts to work around such limitations. I typically write a new script and let any other already handled parts refer to other scripts in the main GVH.
As for more friendly ACS,
1) It would need to be indented and readable properly
2) Compose certain scripts together and maybe make them function on a switch state to reduce the amount of scripts
3) Use switches or for loops instead of a lot of if/elses
...etc
As for feedback on the actual classes, most people find the ice path rather... uh, abusable. It goes on till it hits the end of the map(or a really solid area), it apparently hurts more then intended, especially up close, and multiple times as well as just being neverending, no ammo limitation, no recharging it, or anything.
I agree, the icefiend is fixed (nerfed) in Beta V3.
Most people also find the barbarian's hammer a bit overkill with the magic attack, especially versus Creepers where they just might as well kill themselves, its that effecient versus them.
Not much heard about the worm and the mage (though that mage does remind me ALOT of the oldschool mage from really early GVH, when it was hosted on stlms3 or so maps).
I agree as well, the barbarian hammer is nuts when in the hands of someone who is an expert at playing, but it was beatable (but either way to make it fair, his hammer damage was reduced).
I was still able to lure people and kill them though with other classes even against better people. I'd say the problem is people in GVH just rush and expect things to work, and in this version it requires more 'skill' or less 'one dimensional playing' if you know what I mean.
Oh, you could also join the GVH dev team or invite someone to join in, though dont ask me to let you in, though i technically can its all technical stuff and you're better off asking Euranna. Last time i heard she's around in Skulltag's IRC channel as Rachel, or PM her in the Skulltag forums for more, though its probaly good to have IRC available in case she asks for it.
Heh, its just too much to sign in for, to set up, and a program to install, im no good at that paperwork. :P
If I was to join the dev team, I'd want the new classes to be added and a huge re-write of things done to make it readable

Is Eruanna even contributing anymore?
Edit: Hm, too much non-usefull code stressing servers? Would be nice if you made a list of that, either here or in PM, preferabaly mentioning script number, function and what acs file they're in. Reminds me i should find a lag-free way for GVH11's skycar explosion, but i'm really busy as is with all the GVH changes.
Edit2: Oh, is the Linux glitch fixed yet? Last time i heard someone had an issue with something in GVH's mapinfo, i hope v3b4 will fix that.
To begin:
Who oversaw Santa3b3.pk3?
EDIT:
BTW since you're the lead dev, why haven't you indented all the decorate/ACS code and made it readable? Open source was a great first step, but it's pretty much unreadable unless you're ready to sit down and go through everything.