Copied my T4'd Ninja Blade/Regen/Weapon Mastery Stalker to Beta and respec'd into Reactive Regeneration. My build already included all 9 Regen powers though I did shuffle a few slots around slightly. The overall build didn't need to change much though. This character is very heavy on theme, but I tried to squeeze as much efficiency into the character as possible (Perma Hasten, 42% Smash/Lethal Resists and 20ish other Resists, 90% Slow Resists, only 12% Def to all but Divine Avalanche easily softcaps Melee, good amount of Procs in single target attack chain)
My Beta Experience:
I played several missions ranging from +1/x3 to +4/x8 to experiment with the differences. I normally play Solo around +2 or +3 and keep the player count low, as Stalkers are naturally better at DPSing hard single targets vs groups. Ninja Blade specifically has pretty bad AoE sadly
Playing at lower difficulties was mostly fine, Reactive Regen really helps keeps your health topped up. Regen has always felt like it rides a razor's edge between "unkillable" and "just plain dead". Sometimes a group of enemies could beat on me for eternity and my HP bar never moves. However, if you get too lax about it throughout the mission, your HP can plummet incredibly quickly and then you're dead.
To really stress-test the build, the final mission I played was the Marauder one from Maria Jenkins at +4/x8 which is not normally a mission / difficulty level that I could do on Live. That mission has IDF and since they do -regen, I wanted to see how it would go. Jumping into a group to fight them head on works great for exactly 15 seconds, then MoG wears off and you're dead. So, I used lots of pull tactics. This is where the new Reactive Regen really shined, as I could definitely tell it was helping to both keep me healed up plus prevented a good amount of -regen debuffs from coming through. As long as I was very careful, took it slow, leveraged cooldowns properly, pulling the group around corners, it went OK. I died a few times, though I accepted Death as a natural (but temporary) part of the Regeneration Powerset a long time ago. The mission is still a slog, and clearly I'm not expecting Stalker Regeneration to breeze through this at +4/x8. Ultimately, it was a nice stress-test to get a feel for the Set's ceiling. The -regen resistances and the higher average regen thanks to RR is huge!
When it came time to fight the AV, I had to Rez twice using Second Wind, but I was able to solo the AV without Lore pets or any Temp Powers, though I did use Barrier and Assault Hybrid. As a point of reference, I can solo him just fine on my Live build as well. It's a balance between going heavy DPS while cycling the big protection clicks (Instant Healing, Barrier, MoG) while heavily relying on Divine Avalanche while the big protection clicks are on cooldown. While IH does have superior Regen while it's up, having RR on constantly was definitely preferable.
My Thoughts / Opinions:
The changes are definitely an improvement. I particularly like Reactive Regen, a permanent ~400% Regen (enhanced) at minimum is really nice! I'm also a big fan of the added debuff resistances. Second Wind giving a heal is neat, and I'm fine with the instant rez pop-up on defeat. Glad to see a small amount of +recovery added to Fast Healing, since Stalkers always missed getting that benefit compared to the other archetypes. I didn't really notice the +Damage in MoG, but it's alright (would much rather have +recharge!). While I don't see myself using Instant Healing anymore, shouldn't it also get some -regen resistances? RR can cap -regen resist, but Instant Healing continues to just get neutered.
As other posters have mentioned, the lower HP cap really hurts Stalkers (and by extension Sentinels) a lot here. While going from "fine" to "dead" is kinda part of Regeneration's DNA, it's always felt more extreme on a Stalker, as enemies can burn through their 2k HP much faster. Since increasing the HP cap is unrealistic, it would be really nice to have some kind of +Absorb, though at this stage that's probably a pipe dream. I can live without it.
Please do consider giving +Recharge somewhere though. Especially if you want the Reconstruction + Ailment Resistance bigger heals combo to be an integral part of the set. With Reconstruction being a 60 second cooldown, it needs all the recharge it can get. Since regen has very little Damage Resistance / Defense, it eats through HP much quicker, which continues to be my experience on Live and when testing. In fact, for the longest time I never even had Reconstruction in my build. I always felt like I'd use it, then 5 seconds later I'm at half HP again, so I experimented with other defensive cooldown powers like Unleash Potential and Shadow Meld. Reconstruction just feels like it has a bit of an identity crisis at times. Either your regen is enough to keep you alive forever, or your about to be overwhelmed and need to do something about it. In those cases, popping Reconstruction will buy you a few more seconds at most, so either you need to have it ready again quickly or you need to have a Plan B.
Regardless, I'm happy the set is finally getting some love, thank you Devs! I love the active playstyle of Regeneration and needing to manage incoming damage, but I always find myself reaching to use Reconstruction and MoG only to see them often still recharging on cooldown. If the set could get some +Recharge somewhere, it'd really help with leveraging those active cooldowns (and benefit the players that decide to stick with IH). Reconstruction comboing with Ailment is neat and clearly better than Live, but as a heal in the premier Healing Armor Set, I just wish it did more.