Not great, but oh, it would be so much better if
it could hit a player too. But still, if you go
with the damage/gain life theme, it could be a
decent casual card. In limited, it's a must play
if you're going Black. Direct damage is always a
must play, and you get the bonus of gaining life
with Plague. Nice.
A good limited card doesn't necessarily make for
a good constructed card.
Swallowing Plague is a very good example of an
important removal card in limited play that just
doesn't make the cut in constructed. I used to
draft this card a lot higher, even as a first
pick, but this card's stock has fallen, even in
limited, against cheaper cards that you are more
likely to use more effectively.