This game came out following the great success of Devil Survivor, including in America, and it was probably because of that success abroad that some notable changes were made. Some of this was good, but some of it might have been less well thought out. Please note that there will be unmarked spoilers throughout this review.
Probably the biggest change (probably for American religious sensibilities) was going from a plot centered around the eternal conflict between Law under YHVH and Chaos under the Bels in the first game to one that featured bizarre alien enemies attacking while you used demons to protect yourself. The design for the aliens is in general fine (save for perhaps the ridiculous Dubhe) but without any familiar myth or faith, you have little sense of how awed or fearful your character should be, not even with the entity Polaris which is repeatedly called the ultimate being. Ultimately the major figures of Alcor and Polaris just come off as the poor man's Lucifer and YHVH, and the impending disaster is less fearsome.
The second largest was the structure of events. While it keeps the system of time being consumed as you go to events, the game takes heavily from the Persona series that made Atlus popular in America, which has problems. The emphasis on character interaction means that often you just feel like you're hanging around, not experiencing the apocalypse; and even speeding through text quickly gets dull as the feels like the events are just to speak to one character and then another. There is some defense for this as increases in allies' Fate Levels mean stronger allies and the game is not dependent like the first on keeping one character alive for most of the routes, but what worked in the much longer Persona 4 (70-80 hours) does not nearly so well in this game (30-40 hours).
However, one should not take that to mean that the game is bad. It noted the problems in Devil Survivor and created a better New Game Plus, more skills to use in battle, far fewer of the hated escort missions, a Compendium, better team interaction and more and better demons. It's just that what was done here to improve on Devil Survivor would be used to largely fix the problems of the original in Overclocked, with only the certain character and escort missions mentioned left unresolved.
So I'd say buy the game, but expect it to be good, not incredible.