I played on the development game on 24th of March. Here's some first impressions about the new gameplay:
Build system
The build system makes for much more dynamic maps, which is really great! Varying between stages is great fun, (hopefully) the (public) games won't be 90% of the time focused on tyrant camping anymore. Also, the poor sudden death mechanic is now obsolete as well. It's pretty confusing though, I don't really know how it works. Do for example all the extractors get a reduced percentage as you build a new one close by? How much will the percentages be in the end?
Also, you should make the new percentage appear on the HUD even if an extractor is still building, so you can build chains of extractors much easier. I'm not sure the reduction of build generation over time is required as well, the game seems to be much more dynamic anyway and that change just makes things immensely more complicated. I think it's better to just balance the initial values.
Right now the staging is way too quick, most games the other team gets stage two at about 3 minutes into the game. Also it seems like right now it favours aliens by a great margin, as they are obviously the more mobile/self-sufficient team. The problem is that aliens can right now execute a strategy where everyone goes grangers in the start, build one leech at 100% efficiency each, then evolve straight into dretches to defend the built leeches, leaving maybe one granger in the game building even more leeches. Possible solution? Make grangers unable to evolve to a dretch, or add a timer so evolving isn't instantaneous, and can sometimes even be dangerous.
Also, it seems like due to the asymmetry of the teams the human team needs a lot more builders, which makes fighting in the field for them pretty hard. Since the humans can't defend the extractors as well as aliens unless they build a repeater+armoury+extractor(+node+medi) combo I suggest you tinker around with alien and human extractor build times, right now it's way too slow for humans.
I also noticed that especially getting the overmind down is in pretty much all cases an instant win button, since it's near impossible to recover from the lack of extractors the human team will be causing while the aliens are rebuilding overmind. It's probably pretty much the same with the reactor. I believe this issue needs some work. (Possible solution: make extractors require power/creep before building, but don't explode them when power/creep is taken away, just render them useless with some kind of a corresponding animation)
Other
Marauder is great, i love it! I believe with skilled hands it can now become quite fearsome though, it might need its health toned down, but that remains to be seen later on. Zap is still an issue, zaprushes won serious scrims in GPP 90% of the time, and it will still decimate the reactor area completely. You could tone it down to 50 damage, but I fear even that's not enough. Other aliens have very reasonable changes and play great.
As dodge was mainly built to be a counter for the gpp pounce (well, that's the main use for it anyway, against other attacks it's just cheap), you could really remove it altogether. It's still an annoying ability with not much skill required even if you can't do four of them in a row, and it's even more annoying if you play with higher ping. A useless gimmick promoting gimmicky gameplay. (note that over time I've changed my stance on dodge, I was initially defending it some few years ago, I couldn't dream of that anymore, especially with no alien ability it needs to be used against)
An observation: with current gameplay weapons like lasgun are amazing, since even at stage one you now need a versatile weapon capable of killing fast and efficiently both structures and aliens, so preferably the weapon is hitscan, long range, and even has such a high ammo count as las does.
Flamer in every single game in history has been horrible. I don't think it is a required weapon to include at all.
I heard some rumours about redesigning aliens, I urge you to tread with caution. Aliens in Tremulous are in my opinion with the new changes close to perfect. If you are looking at Natural Selection 2 as an example, which I presume you do, the aliens are much more slower, it's not a versatile system at all as you're always stuck with just one class (90% of the game skulk) and aren't going to have much chances to regain the higher lifeform if you die. Healers like gorge are also very annoying/boring class to play with and against. The upgrades the game has aren't balanced at all, you always want the same upgrades in the same silly order, it might seem like versatile but in reality it's not at all. I find Tremulous aliens much much more better, if it were up to me I'd just redesign the evolve points system, right now you for example get a dragoon, which potentially insta-kills humans way too cheaply. Optionally you could split the differences between classes and their upgrades as different upgrades, (health and secondary attack), but I wouldn't really venture too far into NS2's or any other upgrade system really. I find the Tremulous aliens the best the market has to offer right now.
Overall I'm enjoying the game a lot!
Sorry for grammar and spelling errors,
Meisseli