It can be hard to explain my view on these main arcane casters, and why I've been so focused on summons and their use, but I'll give it a try, for sure, as there have been great posts here. I'll try to give it some structure in easily divided sections - not least so those that want to angrily take issue with any of my views can easily do so via quotes without needing to unpick sections from a larger wall of text.
I'm also going to put aside too big issues - boredom & performance. By the first I mean the endless repeating buff spells which I wanted to do away with by introducing sequencers. By the second I'm referring to the very real performance hits caused by summons and their ai and pathfinding.
Arcane casters, for me, primarily suffer from this not being Pen & Paper, but based upon a pen & paper game. In PnP combat lasts ages, one generally only has a handful of fights, with plenty of role-play (and opportunities to rest) in between. One certainly doesn't slog it out against 200 enemies at a time. In PnP a full spellbook is generally pretty well suited to an action based adventure, whereas here it is exhausted very quickly. Spells that are good just once, against one enemy, like Feeblemind, or Slow, can be a fantastic game changer when used against that one monster your PnP party is currently fighting, but far less useful when it's cast against a single creature in a mob. Right now, just investing in Intimidate will generally be far more useful than having a bunch of these spells to call on.
One solution to this that has been (over)used in infi-casting. Any many know this can lead to cheesy repetitive gameplay, and inevitable nerfs to the spells being used when it proves too efficacious, there is room for it, sure, but for me the joy of being a caster should be finding new and interesting spell combinations and tactics, not charging around blasting everything in sight with the same 3 or 4 spells.
Another has been cooldown abilities (and I've also enjoyed having spell clutch on a recent character), but this can also be far from ideal, as one can find oneself either slow-walking in between, or worse (in my view) rushing through content in a race against the ability duration clock.
From the development side there is the question of balancing spells - so that all of a given level can have a reasonably equal utility - we've done well in that regard but it is essentially a near impossible task. Looking at any given class on Arelith and you'll generally find the same spells being used across many characters, with many others being ignored. We can change them, of course, but that can amount to a zero sum game between the spells - if one wins out, then another will lose out.
Before I start mentioning summons, and my views (partly based upon what I've read here), I can outline what I think -might- work in regard to spells, but given it would be (yet another) departure from core D&D concepts I'd be hesitant. Essentially I'd like to find a a way for generalist wizards and sorcerers to use all schools. Having them draw upon separate reserves would encourage a versatility of use, and give more meaningfulness to specializing. How it would work? Off the top of my head - based upon a new skill introduced to study each one, which would either fill separate spellbooks, or something akin to an arcane flux effect, where once cast a spell could 'flux' into one of a different school, that would become immediately available.
I'm running a bit short of time now and haven't even managed to touch upon summons, and I really wanted to talk a bit about the evil summon list and why it is currently much more powerful, but that will have to wait. What I will first say is that the Summon Creature range of spells WILL be improved, but not to the extent they were last time. Why? Because of my primary issue with summons...
When too powerful they make the summoner, and whatever spells they used entirely superfluous. The actual gameplay becomes using the associate tool to coast along behind your creature, picking up the treasure it leaves behind. I have seen this time and time again in the DM client, and it's maddening.
I absolutely reject the argument (which has been made so many times now) that "Why should we have to actually PLAY such an outdated game? If I was interested in gameplay I wouldn't play a 20 year old game!" Our job as developers should be to make the gameplay challenging and fun, and not simply make a sandbox where people can RP as whatever they choose with minimal effort.
This wandering along behind an all powerful summon (which still happens an awful lot) is just boring as hell, and creates no incentive to discuss, let alone fix up spells and other abilities. Reverting that big change that boosted many summons to god tier? Sadly it had to happen to arrive in this situation - with a problem that desperately needs to be solved we are all focused on doing so. If through overpowered summons, or other abilities we make PvE content a trivial chore we shouldn't be surprised if players' focus switches to PvP. I've played a fair bit on Skal lately, and I love how challenging it remains, for the most part.
I'll likely answer at greater length on this thread soon enough, but right now am being called away from machine.
Thanks for the continued feedback.