Worthy of renting, not buying.
Graphics could've been better. Characters and the environment tend to look ugly at a certain distance. However, the water effects look fantastic. After all, the game IS taken place underwater in a "drowning" civilization.
Some levels may tend to get one nauseous if you hang around too long. Especially when one is looking to complete the game 100% - like me. Collecting things may tend to get frustrating; when you miss a single tonic or audio diary for instance, you have to go ALL the way back to retrieve - very tedious. Nonetheless, the overall flow of the game is great.