Visually, Hydrophobia is gorgeous. The water physics are unlike nothing I've ever seen in a game before and are obviously the highlight of the game. The atmosphere is very well done also, you really feel immersed in this gigantic boat that is sinking as you progress in the story, giving you a claustrophobic feeling.
There was a lot of complaints about the controls back when the game released but now the new control scheme is very intuitive and works very well.
The only downside I think would be the length of the game. It will last about 4-6 hours depending on if you rush through it or try to explore everything. Once you finish it, you can play the Challenge Room or go back to the story to find all the collectibles.
Overall a great downloadable title that lives up to its promises.