1993 PCs have the same gaming power as the iphone 4… that's just awesome.
Sound: perfect porting of the sound but both the music and the sound FX sound compressed unless you use external speakers (well because it's a handheld device earphones)
Gameplay: it has perfect "emulation" for the original game and added online cooperative and online versus. This along with multiple control setups and a few other added features (the biggest one being portability) made this game awesome.
History: doom was the follow up to id software's other big hit "wolfenstein 3D" and both solidified the FPS genre and was cloned many times by other companies. Doom was then ported to just about every system that could handle it for one reason or another and this "tradition" was handed down all the way to the current age which puts us where we are today.
Final feelings: a perfect port of the original game and even better because of its added features, cheap price, and the fact that it's on the phone (meaning it's both on a non-gaming platform and portable).