"Unless" feels like adding come-from (next to goto) to a language. A statement/flow should not change its meaning after being declared/written IMHO.
edit: My criticism is for the suffix version to be clear. Unless / else is actually cool.
edit: My criticism is for the suffix version to be clear. Unless / else is actually cool.
(But it's not remotely like come-from.)
P.S. in re the other response, "unless" is "if not". "until" is "while not".