I couldn't join till late so my feedback is limited to only the 2 maps I played plus Echoes since scoped out the updated version in Forge and I am a fan of that map.
Absolute Zero -
Obviously the first glaring issue with this map was the significant framerate drops, Im not sure if its due to all the water implementation with the geometry or if it is because of the heavy constant scripting, maybe a bit of both. I do love maps that utilize a lot of water and your scripting in the middle is pretty cool, I just wonder if they will ever add any maps into MM that utilize significant scripting such as switches or moving geometry.Deadlock is the only one I can think of in mm that has such scripting and thats because the original Standoff had that feature.
Speaking of scripting your Inceneration cannon behind the scripted door confused almost everyone I think because the switch was too far away from where the weapon is placed and just not obvious enough for players to figure out especially in the middle of a heated battle.
I like the rocket hogs on this map and they were a good choice because I think the regular hogs couldn't be able to pick off players who stay in the upper levels.Speaking of that I noticed some players getting on top of the archways on the edges of the map near the ceiling which is obviously not a good thing and could promote camping so a soft kill atleast is needed up there.
One other slight issue with the map is those low ceiling tunnels; I think those are just awkward for gameplay and can easily be fixed.Also a few elevation changes on the bottom level would be nice but ofcourse you dont want them too effect the flow and driveability of the vehicles too much.
One more minor and easily fixable thing is some of your spawns were confusing, such as the ones facing the steep incline towards the wall, really disorients players.All spawns should face either towards the enemy base or the middle sections of the map and should have a little los and not just have you stare at a wall or incline at spawn.
That's all I can think of for now, hopefully further playtests can tell me more about your map.
Fracture -
This map is obviously pretty polished and I love the overall feel and theme throughout the map. I didnt notice many changes I can think of but that burning Space Suit guy in the chamber is a pretty cool new aesthetic.
I dont know why but for some reason I think your map might make for a really fun infection map as well as BTB.Maybe try it out when that gametype rolls around, just sayin!
Also I noticed that when you were running the flag you Ground Pounded to the bottom bridge with the flag which is a sweet and sneaky option to run the flag through, I really have to try that out in MM!
Overall I like all the weapon placement and I only played this twice so far in MM but it was enjoyable. Very solid map but that's not to say its perfect, I dont know if any map is for that matter, so I do have a couple concerns/ minor gripes if you will.
1) The Mantis like you said acts as a deterrent for players coming through especially through the tunnels but they kind of make the hog feel useless and like going through the tunnel is just a death trap dead end especially when Mantis is operating but I guess thats kind of what you wanted and the whole goal is to take out the mantis first and then in between its respawn, utilize the hog to make flag runs and such so I'm ok with that I suppose. Afterall the mid camo can provide a good option for sneaking up on a pesky defending Mantis.
2) The only other problem I can think of is the snowy ledges near the tunnel entrances, in MM I already seen a couple people abusing that area with the sniper due to its tremendous los looking around either side of that icy pillar and whats worse is you can even get on top of the pillar for extra added protection and nuisance to the enemy team.If the other team is skilled and coordinated I can see the Mantis and Sniper combo in that area being a near impenetrable wall in that area.But luckily there are other options to attack the base besides through the tunnel.
Echoes- Didn't playtest this time but looked the new version over in Forge and it seems like you made some great changes, even though I was already a fan of your original version.
I love the new middle structure and it makes the whole mid area feel new and fresh.Also I really like the teleporter chamber area that has the teleporter that cuts the map in half.That room itself has a great feel to it and feels like a real Forerunner style room, very solid forging.Having said that I can tell with all your great changes to the middle areas that you had to make sacrifices such as roofs of the bases, they dont feel as epic without the Foreunner Spire type roofs you had before, but ofcourse gameplay should always come before aesthetics so you still made a good choice.
Also the banshee spawn structure looks more epic and Forerunner now.I think your map is very solid and even though some might still say its too large or too open but I disagree, not every map needs to have cover at every square inch and be so tightly constructed and it is refreshing for me to see some maps that give the vehicles atleast a decent chance to be and feel powerful.Remember Standoff; Sandtrap, Rats nest, Avalanche?
Lots of long los areas vehicles were an absolute blast but good coordinated teamwork could also counter them, now a days it seems that when a vehicle manages to get more than a few kills in a row some people just assume that its overpowered and there needs to be more cover even though thats not always the case,( for crying out loud the vehicles are almost like paper compared to Halo 3 Vehicles, not too hard to counter). You have pretty nice elevation changes and to me just the right amount of cover but not so much that it makes the vehicles obsolete.
The only thing I can think of is as CDX said some of the mancannons kind of feel like they dont take you effectively anywhere, I guess maybe they shave a few seconds off but not enough to make you feel like its really worth taking them, think Valhalla, now those mancannons you know are worth taking.
But keep up the good work and if I were you I wouldn't change much at this point unless you can afford to bring back the Forerunner Spire look of the bases.If it were up to me I would love to have a map just like this replace Basin which is pretty stale now imo.