TLDR: read the bold text
Overload, in my opinion is not worth slotting in its current state. There are several easily fixable problems that the ultimate has, and since the dev team has clearly been looking at the skill this patch I would like to provide some feedback from myself and several other sorcerers who are experiencing the same issues.
Disclaimer: This is from a mostly PVP perspective and I do not have any information on damage parses using overload and resource return viability in DPS rotations
1. GCD: The ultimate is on the GCD or at least appears to be and it requires time to exit and enter the ultimate. This is a problem because if its intended to be used as a burst tool in pvp, the time it takes to enter the ultimate is more than enough for an enemy to heal out of execute range, activate a reflect/absorb ability etc.... This means that you need to already have the ultimate active when attempting a burst combo which is counter-intuitive. A player should be able to animation cancel a skill into an OL light/heavy attack without a large time gap in between. long story short: the time between pressing the button for the ultimate and being able to activate a light/heavy attack needs to be shorter for it to be useful in pvp burst combo
2. Visibility: the animation for "being in overload" is lightning around your character's hands. The animation for having power surge active is...... lightning around you character's hands. The animation for Boundless storm is..... lightning around you entire character. My point being that without an addon helping you, its rather difficult to tell whether or not you are in overload (especially if using a lightning staff), and in fast paced combat, that's not a mistake you want to make, given ultimate generation is turned off while active. A clear indication of whether or not overload is active would be a welcome quality of life change.
3. Targeting: This one is simple. Overload light attacks can fire without a target in line of sight. there is no reason for this and can cause light attacks to be wasted and fired at nothing or used on an unintended target. People may say this is a L2P issue or that regular staff/weapon light attacks function this way, but overload light attacks have a cost and wasting them seems inconvenient when there is no reason to have it function this way just because weapon light attacks do.
4. Heavy attack usage: The heavy attack damage is very strong, but it is channeled so you cannot use other skills or defend yourself while it is active and it requires you to be fairly close to the targets being hit (even with power overload) and since you are slowed while channeling enemies can easily out-range the heavy attack. I personally use destructive clench, and so am generally fairly close to my target, but many magicka sorcerers are long range casters and actively avoid being close to their target which makes half the overload skill much less desirable for that playstyle. Making the overload heavy attack function similarly to the lightning staff heavy attack would make the heavy attack useful for long range casters and give a strong tool for sorcerer against reflect and absorb skills. (the interaction with roll dodge may be too strong if this were the case, however, and would need to be looked at)
5. Light attack weaving effectiveness: Light attack weaving does not feel rewarding. light attacks had their damage severely reduced, and now do roughly double the damage of a normal light attack. They can be dodged, reflected, absorbed, mitigated by block, and just outright miss the target (see issue #3) while active no ultimate is generated, and each light attack costs 22 ultimate (I believe, I didn't double check this on pts) So you do not net more damage using overload over meteor, atronach, soul assault, or dawnbreaker and the ultimate is sustain damage, not burst. Even though the animations were tightened up in murkmire, weaving OL light attacks still seems clunky and animation cancelling doesn't quite work as it should. Overload only seems useful against magicka characters that don't have reflects or absorbs and run low stamina pools. All told, overload light attack weaving feels awkward, doesn't provide more overall damage than other ultimates, doesn't provide burst damage, is heavily countered by roll dodge, cloak, and reflect/absorb, and needs either a damage buff/cost decrease/ulti-regen enabled/other buff to be be worth slotting/using
6. 3rd Bar: Losing the 3rd bar hit stamina sorcerers and pet sorcerers/healers very hard and they were not compensated for the loss. Both playstyles still suffer from lack of bar space. This could be fixed either by buffing certain sorcerer passives and adjusting the pet system to allow for 1 bar pets, or restoring the overload 3rd bar to one of the morphs.
7. Overload on Stamina: Stamina sorcerers in general do not have any good options for a class ultimate outside of certain situations (negate) but after the 3rd bar removal overload has no place on a stamina sorcerer's bar except for niche build that weaves light attacks into another offensive ultimate such as dawnbreaker, but the users of those builds admit the combo is awkward and difficult to execute properly, and requires not having any defensive ultimate.