Not to be offensive, but you're looking at a bloody thumbnail from one angle in a lineup where I've already admitted that the weapons are not as they will be in the final design. You can't judge the distinctiveness a unit before it is at least rendered in multiple angles.
The hands are intentional, they're humanoid and nostalgic, they have at least decorative hands. If you notice, each hand however is positioned for the task, ahem, at hand - and some of them are incorporated into the weapons themselves.
Does he fire with his arms? Imo no good idea for an AA unit as he would have to lift his arms all the time. Shoulder cannons or something like this (which needs a totally new design though) are the way to go imo...
He does fire with his arms, it is an entirely aesthetic decision which I am unwilling to compromise on. This of all the units should appear almost organic in action, in a twisted YMCA fashion.
Before reading the text I thought he would fire with the left arm...

You also want him to act like a zombie - i.e. when firing he lifts his arms up and holds them in a way the OTA Peewee holds his arms when firing?
The targeting arm will always be moving, actually, collecting data generally. Scripted movement. The rocket launcher, as above noted not of a finalized design, will generally be held at a downward angle, but not directly down, the weapon should bounce during movement and of course will only be raised for firing.
They are all-terrain and so they should look like it and not be bipedal. With the way it is you won't be able to see that they actually are all-terrain lacking a lot of visual communication. Imo spider-like designs are best for all-terrain units - everyone will understand that they can climb up stuff...
Granted, but given good scripting the clambering biped could give a visual experience unseen before in Spring. I did not, however, decide to make them humanoid for any reason of my own, it was a simple directive that the units would be bipedal humanoids.
As I told in the beginning: Way too much similarity to the Peewee. Apart from that you really should think about that tommygun design - well you said the weapons aren't final but well ... imo those tommyguns are as stupid as Mavericks wielding revolvers cowboy style...
At least you realized the weapon statement at this point. The unit is supposed to look like the Spherebot, the latter morphs into it. Similar structure is only logical. The weapons are unpopular it seems - people want something larger and less feasible, currently a chaingun EMG is the most common suggestion.
Well I don't see anything making him different from the other combat units and I wouldn't like to search just for some black/yellow colors in order to find them...
Posture, profile, animations. All things you can't see here. Trust me, he's nothing like the other units, from the visible components to the movement.
So to sum things up in my opinion you should have WAY more diversity in your designs (and that's not just about bipedal or not) as you want to distinguish your units as fast as possible ingame...
They're supposed to be thematically similar but distinguishable. You discount all the elements currently unrevealed in your evaluation. Allow me and those who decide to work on the final designs to surprise you. I'm trying to push humanoid animation, individual effects, posture and the peculiarities of texture to give somewhat similar bodies entirely different appearances, as well as give some scripters a hell of a fun task.