Adding what I've seen of waterfront_preview:

First off - the saferoom. People complain about coughing up dust and blood, the quality of the saferoom and it being basically an old building, and a man named keith marshell is noted to have died (1985 - 2009, 24 years old) - either Ellis' poor poor friend or someone else.

The map begins with going through the building you used a crate to get into. From the general decrepit look of the building, it looks to be abandoned and mostly a maintenance building if anything. Any people who were once here are gone without a trace (likely squatters). The catacombs-esque feel makes me feel almost like I'm walking through the ghosts of a better time.
There is a grate visible after going up a set of stairs which shows a lot of water - after just being near a street before. Not sure if that's anything, I just wanted to mention it.
Continuing forth finds a room with rubble and some fencing, likely as a result of someone disposing of materials. bit by bit (then again I'm not fully sure). A pile of dead is also visible, alongside a missing texture or two.
Before the finale starts, the players are finally greeted with open air at the waterfront - likely docks for the city. A fence needs to be opened, which will trigger a horde. The general waterfront gives off the feeling that this was an evacuation centre to take people to safer places VIA boats - explaining the presence of fencing, a CEDA trailer, vehicles, and mass piles of bodies. The general area is very reminiscent of The Passing's opening chapter.

A ceda graphic can also be found, detailing evacuation centre route designations - of note is a clipping of newspaper reading "green flu shuts airports down", accompanied by an advert about the midnight riders cancelling their tour. There's also a phone directory, a fax paper, and notices saying not to carry firearms. Continuing forward, more dead bodies and tents can be seen, along with piles of luggage, a dead CEDA worker, a Boomer graphic (seen in dead center), and more police barricades. You can also choose to take a path closer to the water's edge, which is less obstructed before it rejoins with the main path.
Further ahead is a generator behind barbed wire fences, more blockades and an entrance underneath an overpass. Continuing forth is even more like The Passing's first chapter, specifically after getting your guns in the store (or maybe akin to bits of Crash Course). Tier 2 weapons and an ammo pile can be found, plus a road up ahead (with missing textures). There are stairs which lead to a very unobstructed path (which leads to an area with nothing in it), and a road which continues further along through all the CEDA stuff before abruptly ending.

My guess is this finale will be a Gauntlet Crescendo, beginning with opening the gate (accompanied with leftover text from Dark Carnival's Carousel Mini Gauntlet Crescendo), forcing players to move on until they reach a helicopter at the end of the waterfront. That, or it's a Gauntlet mixed with a finale, forcing survivors to run to the finale area to disable the alarm, then alert the horde again to signal the chopper (firing flares? who knows?)

That is all I have learned from viewing the last chapter - looks promising, can't wait to see the full thing!

UPDATE FOR THE FULL RELEASE:

So, things I've noticed changed - first off, infected spawn. In map deisgn, the overlook onto water has been cut in the catacombs, and there's now bathrooms! The rubble room feels more like the under-the-river tour of The Passing as well, although the bodies are still present from before (likely meaning this place was still used as a dump for dead bodies in the quarantine zone or something).

The finale starting area is now indoors, and the general feel reminds me of Cold Stream in a way. The run for the chopper, the closed area with supplies... It should be noted both the "open the door" prompt and "talk to the helicopter pilot" prompt appear at the same time - you talk on the radio first.
The gauntlet finale feels like a mix between The Passing and The Parish, with a bit of Cold Stream mixed in, albeit the lack of ammo piles or pipe bombs and boomer biles makes it a bit difficult to fight continuously - something that may be an issue on expert but not on lower difficulties.
The stairs to nowhere I mentioned before have been blocked off, forcing survivors down the main path - complete with fixed textures. There's also a Tank fight here, which stops the flow of commons for a bit. Be careful of the cars, as the Tank can use them.

The area from before where the map abruptly ended has been replaced with a wall and an arrow, leading the survivors to continue through the evacuation centre. An ammo pile, some grenades and guns are up ahead, giving more fuel for the proverbial fire that is the finale.
An area up ahead has wire fences forcing the survivors to take the long way as commons climb over it (stupid of them, they can just run around), very akin to The Parish's Chapter 2 Gauntlet Crescendo.
As the survivors head towards a boat (not a helicopter like the finale starting message and the captions claimed), another Tank spawns, forcing survivors to either backtrack or go around him in the tight outdoor corridors. This is where the last rush kicks in for survivors to get to safety, which is in this case the aforementioned boat.

Upon reaching the boat, the survivors... don't sail away, instead just staying on the boat. I presume it was MEANT to sail away, but it didn't so that sucks.

Some more things I want to point out are the Chapter 2 - 3 saferoom message saying someone will rescue them with a helicopter has been replaced with a message saying the guy now has a stern wheeler - more unique, but the "9 times out of 10 he's dead" message makes a little less sense now.
Also, under the table there is a message from gavin the creatur.

Chapter 3 doesn't have a survival map (although if it did the last section of the finale could work), there are no scavenge maps (still :[ ), and the map is unable to be played in Versus which... also sucks. Aside from the few gripes about gamemodes and the boat not sailing away, this map is... well, it's great! It feels like a Valve map, well and proper, and I would honestly rate it a solid 8/10.

Thanks for the reviews Dom! the boat is made out of brushes so the only way to make it move is using func_tracktrains, which i'm still messing with, and i'm still planning on making a scavenge map after i figure out the boat thing. glad to see you're liking it!

The entire time I've been dropping reviews and pointing out bugs and ♥♥♥♥♥ I've felt like a beta tester, and it's fun doing it in my own time so I figured "why not point out good and bad and hope the dev takes the info to improve the map?"

I was playing the Versus update and I found something in the first chapter.
There's both the buttons to bring the lift down.
AND the radio.

Bug Found: transition from chapter 2 to chapter 3 bugged somehow. Teams swapped again, tank music persisted