This looks nicer than your usual works. I'll take an accurate look..

mmh. I've expected more from the screenshot, there are a lot of things wich needs to be improved but it's for sure you're best map right now.
You should really focus on this, especially on details wich looks kinda "rought". You shouldn't try to match urban_c's detail level. We're in 2014 now.. it's time to go over..
Maya [wich knows a lot about cubes (look at their buildings)] told us that if the world didn't end in 2012 then it's time to build incredible details!

I'll list the things wich hurted my eyes the most [numbers are just to put it easy — random order, there is no priority]

1. choose a theme
   And then follow it. Looking at the landscape's buildings and other details around it seems that we're in the future, but the whole texturing isn't helping a lot to define what's the theme. You should try to give more atmosphere to your maps.
2. the fake water
   A nice effect, but it doesn't look so cool in the flat street where it arrives. There should be some more water on the ground, not the effect disappearing.. it doesn't make sense to me, looks weired. I'd try to model the street and lower it in order to put real water on the flat surface. You can even go further and say that the tank is already half empty, enlarge the hole, deform it on the upper side, make some more scraps and put water inside: you'll have a good camping spot/ half hided pickup
3. those little ramps
   Wich should be cables but still look likes ramps. There is a proper way to do that thing. Anyway if you put teleports you can even put jumppads.
4. the broken glass trick
   1. Glass breaks in quite straight lines and it's very thin. You could have done it in a bigger GP and still thinner.
   2. The same texture on the same wall pretending to be the same glass should look the same, so you should build little rooms behind all those windows. It can be a great way to add some more details and coloured spotlights. And why not, playerstarts.. where they can add something to the gameplay, oc.
5. the sewers
   One level [upper] with less water looking dirty, one leve [lower] with more water looking cleaner than a swimming pool.. it's brighter than anything else if you look it from the upper level.. Anyway the whole thing, even if it looks good, it's not well designed to me. Too straight.. campish, boring. You should improve them a lot thinking to something wich adds a level of gameplay. What about a huge hole somewhere in the streets wich links all the levels? could be a great gameplay add if put in the right corner of the central building cuz it would show all the map height in just one blink.
6. those huge doors
   The shape is ..mmh.. dunno, but the light.. just comes from nowhere! :P give us lightspots! [will look cool if you put them in the ground] AND they seem to be cutted in the wall's texture... mmh.. some kind of frame? no? little lit? no? :|
7. central building of the bigger area
   makes no sense. There are several things wich doesn't collide where they should, textures wich miss their continuation on the other side.. the floors seems to be wooden and so you put a wooden stripe outside. But you forgot to make them all the same height! Can't you just use the grid and copy>paste such things? meh :/ The quad's room isn't even high enought to jump. You should really put some effort in that building.. it's the center of your map.
8. emergency stairs
   leading nowhere. all ppl died in flames.. not so cool. Put some more details on them too. Such structures should be very light, use thinner frames then.. no more cubes needed, just thinner. It will look way and way better.
9. the fallen piece of building
   really looks like a strange wooden building in the middle of the street. If you think you need something there why don' you just link the sides of the street with another lower building? you can make a some parking slots in the piece of street that you earn. Plus you won't have the oblique piece of street you hate so much [i've noticed many not nice things where cubes should merge..].
   and don't use one big fire particle, place more but little.. it's not nice that way
10. this
    looks really horrible. not just the "lion-head-decoration" texture, even the wall's and how you merged them in single cubes.. it's horrible.. do it by indenting the decorative-texture's section. And change it in the stairs cuz it's obviously horizontal.
11. 45° stairs
    most of the stairs around the map are 45°. Now, in the real world you see such stairs just in very old buildings, like castles' towers.. in sauer, where you're some kind of beast wich walks 100km/h and jumps 10 meters long you can't put such stairs, you always hit the ceiling running down.
12. there is an error
    in the quad room, where the stairs gets into the wall, those that actually lets you reach the quad, cuz the others are just for the healthboost... the biggest thing in the middle.. but from the quad room you can get the healthboost in just one jump; that's the real error :/
13. the spikes
    wich kills you with a monster's gun sound. actually there are all the other player tryn' to kill you, it's quite enought.. plus those spikes kills the gameplay a lot because pratically avoid duels on the streets.
14. that so long wooden ramp
    it looks longer than an highway, it's longer than 2 of your tanks.. faces gravity well.. and ends framed in the fallen building. just to say
15. the tanks
    the model may look ok but the texture is mmh, like 12x12px? less? I think I can count them even running on it shooting ppl.. just no.
16. graffitis/murals
    mmh.. no? it's a good idea but give us more background-feeling with them. back to point 1.
    some of them are higher than the streets' lamps, who's supposed to read them? godzilla?

I've spent a lot of time on your map and I still can't figuer out how good [or bad] the gameplay will be.. but since I've already spent a lot of time I won't test it.. I wrote a lot, and I've been detailed.. don't crush my review.
Your map is [cites meow] one step away from beeing good.
then whose step is it is another question.. maybe for your map is more likely a cloverfield-big-monster's step but as far as I can see you have no fear in facing the hardwork.
Don't start other things. Go on with this.
And maybe sometimes join some coopedit :3

It took me so much time that while I was writing this I've fed the dogs, then [almost not] seen 2 episodes of babylon 5 and cooked and ate dinner.
phew..

And I've even merged some points..