How easy is it to come to terms with the interface and start playing games?
I want to say pretty easy overall, however when it comes to playing games with someone else online you both need to have the same add-ons available, otherwise your not going to be able to load all of the model assets.
As long as you have that part covered, and I've yet to have a time where one person had something that another person could not get in the span of five minutes or less, then the system itself just takes some getting used to.
Are you also able to play games over a protracted length of time, in that say during a lunch break you could get a movement or shooting phase in?
I want to say yes, when you have an understanding of the system the turn phases only take slightly longer than their real world counterparts (and that only really happens because its slightly harder to right certain models if they fall over.)