As the best Vampire Commander for relentless pressure, its all about keeping the heat on
Well, those who play mill will love it - everyone else will be sick of seeing their expertly-crafted decks end up in their graveyard
Conversely, if a permanent is sacrificed during the resolution of a spell or ability, that spell or ability will finish resolving before Carmen, Cruel Skymarcher's second ability is put onto the stack
Every 1,000 XP nets you one Mastery level on the Mastery track, and each level has the possibility for extra goodies
The highest difficulty isn't particularly high if you have even half an on-meta deck of your own (speaking as a lapsed, at most casual TCG player myself), and so once you know what you're doing they can get a bit repetitive
Developing a Commander deck can be rather time-consuming