Now, I don't comment here(much) these days, but I feel I should comment on this. I've been an avid class collector for a long time, and I enjoy revolving my different classes. I enjoy having that variety for different purposes, however I have some classes that feel...off, these days. I want to start with discussing potential issues with regens, model, and enhancements. I'm sure that these have been covered before, but every voice makes a difference. I'm going to be stating from my purely subjective experience with how classes tend to feel. If anyone wants me to specifically test any classes to give a feel, I have a large variety of them, and I intend to be watching this thread.
Warrior mana regen is generally underwhelming in the system as it is, due largely in part due to the warrior model and fighter enhancements having the haste of a brick. When relying on hitting, and being hit, to generate mana, a slow hit rate can cause very bad stuttering in skills, and can make it hard to enjoy some classes, especially those with below average speed such as Glacial Warlord. I recognize that the speed difference is compensated by damage increase, but it makes the class feel sluggish, and hard to control. I've experienced this issue with other warrior model classes, although Glacial Warlord was an extreme. A potential fix to this is giving some method of increasing haste, although that depends on balancing and whatnot.
Thief/rogue mana regen tends to be helpful...so long as you're alone. When you have other people, I find that it tends to drop massively due to a lack of being targeted. While the dodge rate and haste are often spectacular if not insane on a thief model with thief enhancements, there are issues when using in multiplayer that I've experienced. Coupled with some high mana costs, many rogue regen classes can suffer if you're not careful, and even in duos can create large mana issues. I've experienced this plenty with my Blade Master, which I use as a lovely support(I realize there are better out there) due to the Sever ability. While more difficult, a suggestion might be to implement either a higher mana income on hitting your target or rebalancing mana costs to consider the multiplayer aspects of this model. Naval Command also suffers heavily from mana issues, in my experience, due to the fact its a party class with a poor dodge rate, that uses thief regen.
Mage mana regen has become the norm, with so many classes being built on crits. However, it is still a highly fluid regen, as I've found with my original Dark Caster Class. With a low crit rate, however, the mana regen can still suffer without an HP-to-MP conversion skill. I prefer to use wizard enhancements on mage class models, regardless of the crit rate, as the base damage is improved, and I prefer the reliable noncrits. One suggestion for this mana regen model is to scale it to non-crit values primarily, where you can have a steady flow with noncrits, while the uncommon/rare crit provide massive bursts. I realize this would likely be difficult to do, but would likely help in leaning away from crit reliance.
Mana regens that rely on a skill effect to be active, in my experience, have always been poor and unenjoyable to use. I often find it hard to keep the skill up and regain mana, due to it effectively relying on the standard warrior regen with a mana input. A simple suggestion to this would be to improve the regen rate so the generally poor crit crate is providing a steady flow of mana. I find most of these classes to already have high mana costs, which only makes it harder to manage mana properly, and potentially frustrating.
Hybrid models are nice, and allow for choice between how you want to build, but their respective enhancement falls short. I find the Hybrid enhancement to be highly underwhelming, and the Spellbreaker isn't much better in my experience. I tend to sway towards wizard on physical/magical hybrid classes due to the general better boost to everything I felt with the wizard enhancements. I'm unsure how to improve this, other than generally providing better haste and damage increases than it does now.
Luck models are...well, interesting. Perhaps making them function as intended and relying on the Luck stat would be best, similar to how mages are meant to function and rely on Int/Wis.
Overall, my biggest problem I find is the non-crit mana flow. I find that it is generally underwhelming in most cases, and that leads to classes suffering in their enjoyment.
These are my thoughts an opinions regarding classes. I have not sat down to test on the testing servers, but these comments are how I've felt on the current live servers. I apologize if I missed anything, and I do hope this helps! Have a good day, and thank you for reading!