Krogan Soldier is actually pretty fun to play. I play mine with a Widow, GPS, and full melee talents, maxing out everything and skipping Carnage altogether, and he's a pretty versatile Silver character. I can pick off guys with headshots, and when it's appropriate, charge into the fray and wreck havoc. Once raged up, I can one shot almost anything on silver besides elite mobs and some of the smaller guys like Ravagers, Pyros and Phantoms, and the latter two get staggered enough where the second hit is easy and safe. Inferno Grenades are fun to use on groups. The GPS is great up to a certain point, then the Widow destroys everything past that. It's not a character I want to take into Gold, but neither do I want or need to. The gameplay is fun and varied enough on Silver.
Turian Soldiers on the other hand...it can be summed up as "Press 1 and hold down the Revenant". That's basically all it really can do. What would've helped the class is if Marksman had an evolution to allow an extra power to be used, as AR does, but nope. And even though Marksman + Turian has great synergy with the Revenant, it still doesn't make it interesting or fun.