I saw the play for the first time with the new cast, so I can't speak to the differences, but I thought everyone was wonderful and don't immediately see how the original cast members could have been better. Funny and touching, absolutely.
I found it hard not to compare this to "Moscow, Moscow..." for obvious reasons. Whereas that play seemed like a one-joke riff that stayed on the surface (and was pretty forgettable), I felt like "Life Sucks" truly refashioned Chekhov's world into a new contemporary play with depth, humor, profundity. I recommend it.