Jacob's Ladder is one of my favorite movies and for me the most mind-blowing ending ever. More recently we've had many movies that somehow had the same idea for an ending (don't want to mention them so not to spoil Jacob's Ladder) but AFAIK this was the first time that it was used.
I love Jacob's Ladder to death, despite the fact that it once gave me vivid nightmares. Or maybe because of that.
But the ending really sucks. The last minute of the film just fucks the whole thing up by being so simplistic--in a sense it makes the whole movie easy to dismiss. It should just end at the stairway.
I haven't seen it since it was in the cinemas but I remember at the time it made a big impact on me. For some reason, I always link it with Angel Heart, in terms of that impact.