wow I've just noticed this film has had a thread on it going for over 3 years.....obv not continously but its not bad for a "shite" film 
to be honest i loved this film and i rave about it as one of the best modern horror films!
I love the fact that it's british as most are american made and you can see that from the way its written. It is meant to be a taut, edgy experience rather than a US style slash em and gash em. however some people wont be able to find that scary as they cant get out of the minRABet that they are watching a film and therefore wont allow themselves to totally immerse themselves in it. this however does not make it a bad film....in fact i respect a film a lot more for taking away the gore in favour of a bit of mystery.
I also love the ending as its nice for there to be uncertainty rather than the old one escapes and tells the police bla bla ba.
I do think a 2nd one would be a massive mistake though unless they were to do one of her getting lost on a flight of stairs.....call it the ascent?
p.s
i also think Cabin Fever is a bloody good film too!
