The Soviets are like if PE and US crashed into each other. They're highly mobile with little static defense, but while they have MG's and Tanks, they're not as solid as Ostheer's.
Half my problems with Soviet are that the faction design is severely flawed, imo. They have no vehicular mid-game, so they must hold off with AT Grenades and ZiS guns until they can get Tanks.
And thanks to their faction design, you simply can not give them said vehicles, because their buildings are literally separated by early-game and late-game, there is no middle tier to which you could add a BA-64 or something.
There is a recurring suggested fix for the Soviets that would greatly help with their mid game problems. It is to swap the SU76 to T3 and the T34 to T4, greatly reduce the fuel costs for T3 and increase the fuel costs of T4 (might also need a slight increase to T1 and T2 to slow down T3, without overpricing T4 tho). This way, T3 comes a little earlier, Soviets have a halftrack to reinforce from a little sooner, the T70 and SU75 come earlier to deal with the light and medium vehicles of the germans, and give them some breakthrough capabilities vs turtling germans a little earlier as well. While the T4 then has a synergy between the T34 and SU85. It's the perfect fix, which after some balancing, will provide the soviets with a healthy mid to late game and also improve their combined arms tactics.
EDIT: such a change would also allow for better call-in oriented tactics, like stalling at T3 for your call in tanks; or for a more infantry oriented commander, skip T3 and stall for T4 vehicles. The key here is that both T3 and T4 would provide a mix of units which compliment one another at different stages of the game, instead of the current all "offense" of T3 or all "defense" of T4.
Here is a Reddit thread detailing the suggested changes:
http://www.reddit.com/r/CompanyOfHeroes/comments/21jmvg/so_regardless_of_the_early_game_which_has_reach_a/