Mana-concerns aside for the moment (they're very complex, and most people would rather see mana not exist at all in the game)...
Viper Strike v2 is way worse than v1. There really ought to be a solid "melee casting" skill that scales strongly with +skills and doesn't rely on weapon dps (like EA for bows, or like every damaging spell). I'm still perplexed as to why they changed it in the first place, let alone why they changed it fundamentally from a +skill scalar to a dps scalar.
Double Strike (really most of the pure single targets) is completely outclassed by stuff like MS and SS now. GGG needs to do something to keep up with the power creep, be it nerfing the high stuff or buffing the low stuff.
Sweep is also in the "outclassed by SS" camp. Same as above.
Elemental Hit needs a complete rework. Flat elemental damage isn't rare anymore with Wrath, Anger, Herald of Ice, Herald of Thunder. Inherent crit chance from quality is no better than, say, Flicker Strike. It needs something unique about it, not sure what.
Firestorm is insanely strong if you have really high gem quality and Enhance. I kinda wish that the difference between 0qual and 20qual wasn't so huge. It certainly doesn't need any kind of blanket buff because it is one of the strongest skills in the game with the right setup.
Flame Surge would be kinda fun as a line-casted skill. Still thin, but really long reach. I completely disagree with the "just make it a projectile" line of thinking. We should want skills to be different, not more of the same. Besides that, it's strong as hell.
Storm Call has weird desync that depends entirely on your cast speed. If it falls on certain breakpoints, it's fine. If not, it desyncs like mad. Honestly no clue how to fix this, but it's an engine issue primarily.
Summon Skeletons has a ton of love. I wish they were a little bit faster and that there was some way to dedicate a summoner to skeletons/VSS. Something like "cannot summon non-skeletons; double max skeletons;". Would be a cool unique.
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"Fun" is not a winner-takes-all game.
"[1.3.0] Too Many Clones! -- PvE Templar Archer Summoner": /view-thread/1127263