If you go and look up Exquisite Archangel in
Gatherer, you'll find that its rulings include a
reminder that its ability counts as gaining life
and a delightfully understated comment that
"Other cards that interact with life gain or
life loss will interact with this effect
accordingly". That's as good as a link that
leads to the pages for Ajani's Pridemate and
Well of Lost Dreams. Of course, we tend to use
cards like this in Commander where it's not
effective against accumulated commander damage
or Door to Nothingness, which is kind of a
downer, but there are still enough applications
for the Archangel that I don't doubt it'll see a
lot of casual play.
Exquisite Archangel bears
some similarity to
Mirrodin’s Platinum Angel: both keep
you from losing the game, both fly, and both
cost seven mana to get this. Exquisite Archangel
trades the artifact type for better combat stats
and a color.
In combat, the Archangel
does about what you’d want: fly over and kill.
5/5 flying for 7 is about what white gets
normally, and this makes for a scarily effective
clock in Limited formats once you get there.
It’s too slow for other formats except
Commander, where a relevant creature type and
being big helps it out.
The effect…it's not awful,
but it’s nowhere near as awesome as it sounds.
You basically trade Exquisite Angel for a
refresh of your life total if you’d lose; this
makes it useful if you’re going to die to combat
damage, but you do lose the 5/5 that might help
you out of it (and you do nothing to their board
state). And if you were going to lose either by
decking out or poison, this merely buys you a
turn in the former’s case and does nothing in
the latter's case. The effect is flashy and
deserving of mythic status, and it's a nice
bonus, but it really isn’t as amazing as it
sounds, unless it's buying you the one turn you
need to win the game.