Very underwhelming in my opinion.
It feels overall, like they're trying to cram even more functionality into his kit, leaving it overly complex, situational and redundant. I really need to try it out for myself in an uncontrolled environment, before I can say "yeh" or "meh", but the demonstation didn't impress me. Vauban also seem to become less and less of a trapper/sapper thematically, and his abilities still aren't all that useful in missions, where we're constantly racing frantically to objectives and the extraction zone, while nuking everything in and out of sight. How about designing certain frames around functionality/combat roles, instead of homogenizing performance in generic environments. Vauban would be an excellent defensive frame, if his kit had some proper, lethal traps, that scaled well, and could be deployed to create chokepoints and killing grounds. Right now, however, he just seem like a gimmick chucker with a few new flashy tricks.
I have two main uses for Ember:
First, I use her for swarm control, and she can do that anywhere on the starchart. Especially in invasions and maps comprising of cramped spaces like Eris, she's able to either outright clear out the mob carpets, or stun the hardier mobs for long enough to bring down with weapons fire. Certain other frames can do it as well, and some are even better at it. But overall, I find her kit useful and easy to manage. And she sets things on fire... That's a plus!
The new build looks like a huge nerf in this regard. Now I need to spam abilities constantly for the same effect, burning through energy at alarming rates, depending on cost (of ability 4, mind you). I need line of sight, making things like elevation and obstructing terrain far bigger factors. On top of that, I now have another meter to manage (which needs the casting of another ability to lower, adding to the energy consumption). And should I now be in a situation, where I need to pay close attention to other things in the environment (squad mates, objectives, etc...), I risk losing all my energy... as a caster frame..... Yeeeeah...
Second: I suffer from chronic pain in a majority of my joints. Some days are relatively good, and some days are bad. Sometimes I just need a frame, that'll get the job done with a minimum of effort, and in that regard, Ember does well. I don't need to see orange numbers on the mission summary, I just need to pull my weight and get the job done. And now I can't use her for that. I guess I'll switch over to my Saryn or Equinox instead.
In all seriousness, you didn't really need to change her kit all that much. I get it. You want to make her more viable in high end content, and you want more player engagement. Well, what if you instead created more synergy between her abilities, let her forego of one thing to augment another...
If you look at fireball functionality, it has somewhat of a double cost for charging up, eating up both additional energy and time, resulting in a much lower dps as well as a window of vulnerability, where you are doing nothing to stop enemies from trying to kill you. How about if damage/charge time increases and energy/charge time decreases to reward what is essentially an investment of dps. Right now, the lost dps for charging up doesn't feel it gets much of a payoff. If instead the damage increased somewhat exponentially (to a certain point), and energy cost increased at a slower rate, it would pay off for not firing or using other abilities actively. Maybe even let you hold the fireball while moving into a better position (add restrictions to amount of time, sprinting/movement, energy gain to avoid exploitation).
Accelerant already synergizes quite well with the rest of Ember's kit. A possible addition could be the ability to charge up the ability for extra range, as well as increased heat proc chance on affected enemies.
One lament I see a lot is WoF's reduced range. Well, what if you could increase that range with fireblast? A normal key tap would create a mormal effect. Holding the key down would create an expanding ring of fire, immolating everything in its wake, and pushing the area of an active WoF outwards (which over time would shrink back to normal). Remember, that one of the primary gripes with Ember pre-nerf was her ability to bullet jump through a mission, incinerating entire tiles in the process, hence the nerf to her range? Well, while getting more area range, being locked down in a charge-up animation will make that less favorable in a rush through a mission. Right now, simply stopping to pick up an ayatan star will put you so far behind, that the rest of the squad has killed everything on the map, when you catch up, regardless of you being an Ember or other map nuker.
World on Fire doesn't really need much of a buff, if the rest of Ember's kit gets to synergize better with it. The new armour reduction from heat procs should make her more viable in higher end content in any case.
Right now, with the changes as they were shown, even with tweaks like the increased range on her passive, my Ember is going to get shelved for a loooong time. She won't be doing what I need her to do, and other frames can fill that functionality with a minimum of adjustment. And functionality as well as fun dictates, in the end, which frame I bring to a mission, and Ember's new kit doesn't seem like fun to me.
Perhaps her next overhaul will make her viable again.
There's another thing with these changes nagging me as well: Orbital strikes... and comets... working indoors..... From an immersion standpoint, that's... bad. To me, that is a major turn off. And to whoever decides do quip "space magic" in response, I just have to say "Where's my robe and wizard hat?".