just buy it. it's the best side scroller from it's period ever, possibly even still. you can not compare it to many other games for the sheer excitement, fun, and action that is going on. I spent wayyyyyy too much time with it after I bought it (last night). So much in fact I was an hour late for work today due to oversleeping.
Unless you have something important coming up before Christmas, then wait because you won't want to play much else or do much else for a little while.