The hardest part of the Water Temple is that one of the keys is hidden way better than the others, and if you start opening doors in the wrong direction you will run out of keys without it. Combine that with the clunkiness of swapping to/from the Iron Boots and raising/lowering the water level, and the place quickly grew tedious and frustrating.
The 3DS remake added an extra camera sweep and some decor highlighting the hidden passage where that key is found.
I'll point out that you can use Dragon Age Keep to plan out key choices in the narratives of the first two games, and even create a world state for import into Inquisition. Helpful if you want to play Inquisition and want a refresher and/or don't want to replay the earlier games