Think cockatrice that trades ergonomics for a rules engine. Much easier to play when the game just 'works'. It even has loop detection for when you go infinite with triggers.
One thing to note is the community run servers are plagued with performance hitches at peak time. If you play regularly on xmage with friends, I'd recommend making an image on your preferred VPS provider and spinning up an instance when y'all want to play.
Apparently since you can construct a Turing machine in Magic: The Gathering, this is a case where halting is formally undecidable in general. :-)
(not to suggest that any actual players have ever achieved a position in real play that would be undecidable by this engine)
[0] https://scryfall.com/card/pvan/304/oracle?utm_source=mw_MTGW...
Me and my friends have found that the most fun is to play using https://github.com/dr4fters/dr4ft (dr4ft.info, currently down, mirror here: https://beta-dr4ft.herokuapp.com/#) - we do a draft, then do a best of 3 rounds with the decks that we make. It makes deck-building a core part of the game, and it's always a completely new game. Brilliant fun.
Also, so much effort ><