OutRun Online Arcade is OutRun. Did you like OutRun last time you played it? Do you like it enough to pay 800 MS Points for it and rack up some Achievements? Do you like it enough to play against your friends? These are the questions you must ask yourself before buying, if you haven't taken the plunge already, of course.
As far as this reviewer is concerned, if you haven't played the game already, then you really owe it to yourself to give it a try. However, if you've played OutRun many times over the years, then you'll need to ask yourself if Online Arcade is offering anything other than what you've seen countless times before.