I've tried Sustagen but it's overly sweet. If I'm going to indulge in a chocolate drink (which really is almost never) then I'll drink a hot European style chocolate which is custard in texture and consistency.
However, it's a great supplement for really ill people who are unable to eat or get enough nutrients into their bodies. Both my father and father in law (who have both passed away from cancer) were made to drink Sustagen to aid with supplement intake but more so as they were both terminal to provide calories for their weakened bodies. My father hated the taste and hated drinking it. Needless to say, after 3 years my mum still has a large tin of Sustagen sitting in the pantry - last opened when my dad was still alive.