The (un)holy lovechild of a pair of Defenders, a Stormclad, a Cyclone, and a pack of Stormcallers.
Honestly, I'm fairly happy with our first Colossus (there may well be more on the horizon someday). It's got a lot of potential, and syngery with just about every caster we have. Two of our strongest guns, a pair of medium strength multi-shot guns, with a superb anti-infantry passive, and two fists swinging about the highest base P+S we can muster at the moment. Based on those alone, I'd of considered the jack a success, but it has electro-leap (not overly useful, but it's there) and the Storm Pods and all of the tactical/synergistic avenues that it opens up as well.
For all it's shooting potential, Stormwall is not the be-all end-all jack. It's ranged firepower is quite justified for the cost, but it's melee, though absolutely solid, isn't why people will bring it. For all it's mighty Pow 20 fists, it's still barely more effective than a Stormclad, Rowdy, or even an Ironclad.
All told, good enough. Slightly lower Mat, which is an issue, but solid armor, good # of boxes, average speed... not much more you could really ask for. As Arcane Shield or similar is almost always going to be on it, it's more than a little resistant when combined with nearly double the boxes of an Ironclad.
In melee, your standard Stormwall is only somewhat more efficient than Rowdy. Though this can go up significantly with the right support/casters, it's important to remember that with standard focus limitations, a Stormwall only has +1 POW over a Stormclad. Your still likely to trash most heavies with a full focus load, but the slightly lower MAT may cause issues. Rowdy, between Counter-Charge, MAT 8, and Aggressive, is somewhat more efficient, though he doesn't quite hit as hard.
Voltaic Fists: Good Solid beatstick, with built-in reach and open hands for throws as needed. Combined with it's mighty Strength, you can chuck a model a good ways. Electro-leap is purely superfluous, though may interact with the thresher 'Sweep' power attack for fun times if infantry attempt to swarm it.
'Big Guns': Slightly shorter range than a Defender, but you have two. The Firing Arcs may be problematic, but I doubt many will have a trouble. Net result is slightly less potency than a Stormstrider, but untyped damage is helpful, and readily availability of boosting are better than the oft-chaotic electro-leaps.
Iron Storms: It's a Cyclone, only... BETTER! No more *Action for the templates, if your using the Big Guns, you can drop the templates too. Or drop one template, and shoot with the other gun, it's very flexible.
Storm Pods: Not really a 'weapon' system, but close enough. Drop a Pod completely within 10", then zap stuff in-between the pod and the Stormwall. Jacks can be disrupted if they damage them, and the damage is boostable. This goes off regardless of if your swinging your fists or shooting the guns. Dropping models, even small base ones, is always a good thing. If your opponent has no ranged threats, or if they are out of position, you can also use the pods to block and jam, though they won't ever engage.
Additionally, they function as if they were Stormcallers for Triangulation purposes, thus it may be advantageous to drop the first pod in your own field of influence rather than be aggressive with them. Note, the lightning bolt between the pods and Stormwall is not an attack, and thus bypasses many defenses, and can be boosted, but does not automatically disrupt so heavier armor can prevent a jack from being disrupted.
Storm Pods are dropped the moment the Stormwall finishes moving, you can then pick up and throw them using a Throw power attack out to a significant range. Not always going to be useful, but it would generate a pow 17 hit on whatever small base model you throw it at. It's something to consider.