the soundengine has some flaws, like being easy to clip etc.. also i find that e.g. the fm engine is hard to use for me, because the ui is quite cryptical, compared to the other engines.
i use the op-1 for both, live and studio work. in a live context i make use of nearly everything: drumsampler, synths and tape with prerecorded athmos. i considered using the tape as a live looper, but the ehx2880 just outperforms the op-1 tape...
in studio i use the sequencers and the one or the other lo-fi sound.
i must admit that after a few weeks, the machine lost some of it's glamour. but what remains is what it is: a powerful collection of features packed in a handy and beautiful box. though it does not sound really good (it's still not an access virus ; edit: or any other modern VA, i'm not advertising here ..), i absolutely love it.