Woaah. This is perfect. I really love dark themed stuff like this, especially when the action come in at 1:52! I think it actually sounds full enough. More instruments would really make it messy and all.
My favorite part is at the end with the piano, for sure.
The rain sample is actually a good filler (for the high freq). It sounds quite strange as a listener if it suddenly fades away due to the fact that the rain sample is taking a lot of attention (to me at least).
All in all, this is such a masterpiece. Excellent work.