Seemed to. I couldn't tell you it was lightning fast, but it definitely went around corners without too much hassle.
Marino Franchitti described it as the most stable car he's driven over the bumps of Sebring (of which there are far more, than at say, Le-Mans).
The opinion right now seems to be that the theory seems to work out as expected - but as with any new car, there are issues - they're working through those issues and hope to be well and truly ready for Le-Mans.
In the days after Sebring they tested alongside Audi, and completed an entire stint (about an hour and a bit) without any issues.
Can they run for 24hrs? who knows. Can they produce enough speed to be competitive? Who knows. One thing does seem certain though - the Deltawing is not about outright speed, but enough speed to leave them a number of pitstops up at the end of a race. Remember, this car only produces 300 odd horsepower - it's not likely to be as fast as something like the Audi - they're racing on the basis of the Tortoise vs Hare.