I tried Credit Karma this year - I was lucky in that one of the first forms I went to enter wasn't supported. I had a 1099-R from a Roth distribution that wasn't taxable (withdrawal of contribution), and on the 1099-R the "Taxable Amount Not Determined" box was checked (I'm assuming this is checked because they don't know your Roth basis, so you have to figure this out yourself on form 8606).
That checkbox was not supported in CreditKarma. Womp womp, on to the next provider on the list to try this year. So far I have been pretty happy with FreeTaxUSA, and I'm almost done (just need to get my 1099s from Vanguard).
$0 for federal, no matter how complicated. $12.95 for State, and I got a coupon for 10% off that.