Good, Fun, Great Graphics but much too short.
Many shooters for the apple store are shocking, but this is definitely worth while. It may not be worth the $8.99 price but is sure close. I had played it on the iPod Touch 4 and was able to use the retina screen to its advantages. Even some smudge marks from my fingers didn't diminish its effect. Its gameplay is true to the console with a few minor edits for fluency and portability.
For me it was short I had actually completed it in school, breaking it up in-between classes and lunch. The story was fine for the most part, I don't have any particular problems with it. It may be that I was just fast in completing it but for anyone who likes the series or who isn't to bad with iPod controls should have any problem with it.
To finish the review the only real problem that I had found with it was it was too short for the price. For $8.99 you would expect something a bit longer but for and app store game it is much better than expected.