I'm no goaltending expert by any stretch of the imagination, but most goalies you see are quite aggressive and come out of the net to take away angles etc and that's their style. Allen on the other hand seem to sometimes come out and sometimes stay deep. He also seems to get his angles wrong, exposing the goal.
Like Kane's first last night. Kane entered the zone centrally and Allen is, correctly, central in the goal, albeit quite deep, well inside the crease, but when Kane moves over to his left, Allen's right, Allen doesn't follow and does not come out, leaving space on his blocker side. I thought that was very weird why he acted like that.
Does he not know where he is in the goal? Did he read the play badly and didn't expect a shot (is he generally bad at reading the game)?
Either way, I think his positioning is off quite often.
I would add to Robb's astute analysis the following:
Jake's positive attributes
1. Very fast legs (although I think this becomes a double edged sword for him at times)
2. Good glove hand (although I would typically expect better--ala Rinne---from someone with his reflexes)
Jake's Inconsistencies
1. Vision--Puck Tracking--I don't think he sees/tracks the puck as well as the elite goaltenders.
2. Overreliance on the butterfly slide as opposed side shuffle for lateral movement---Too fast to his knees
3. Generally inconsistent positioning (sometimes Ok but too often he gets in bad positions)
4. At this point, lack of confidence which translates to his style becoming a mishmash and not having confidence in any particular fundamental. (Example--he seems to be playing deeper in net this year which I doubt will work out well for him over the course of a season)
5. When things are going really badly for him, he starts cheating and doing butterfly slides to where he thinks the shot is heading.
I labelled the second list "inconsistencies" b/c there are times when these attributes are less of a problem. For example, on the play in which he was injured last night, I think he played the puck very well from start to finish. The key is to get that level of execution on the vast majority of shots he faces per night.
Over the course of the last 18 months or so, though, I think the many dips have shot his confidence to a degree that these problems have been more prevalent. He seems to panic more quickly now and show his hand to the shooter (he reacts before the shooter shoots or passes) and NHL shooters are so good that they can take advantage of an early move by the goaltender.
In any case, Jake may get it together and start playing well. I think a good stretch of play is what he needs more than anything else, mainly for his confidence.