Played several games with the SSU this weekend. They are not overpowered as someone from anther board has strenuously stated
They do play very differently than the Axis or Allies though. Two MGs in their battle squad along with the short ranged rifles was pretty cool. They could throw out 12 attacks if within 2 squares, but still a very solid 6 if within 4 squares. The Helicopted had no luck, as it kept getting pwn3d by my ridiculous luck with the Heavy Flak Grenadiers. Koshka and Grandma are pretty awesome, and the combo of Assault and Fighting spirit can really kick som butt if you set things up right. Our forces were all of the SSU releases vs the Axis Revised core + a Kommando truppe. One issue that came up is that the SSU engineer can't bring Grandma back since its a rare unit, but this won't be a big deal when the rest of the walkers come out.
I think once the KV-47 with dual howitzers and All in One comes out, the SSU won't have any big troubles against walkers.