Given my very long and somewhat sordid history in the Mega Man world, feel free to take what I'm about to say with a grain of salt if you're a fan of this series.
Mega Man Battle Network 5 is the latest in the series with the exception of the recently unveiled Mega Man Battle Network 5: Double Team for the Nintendo DS. However, in what can be considered a common Capcom business practice, the game fails in virtually any way to provide an experience even remotely different from its predecessors. The graphics engine is almost completely identical, the music has the same set of Game Boy Advance instrument samples, and the battle system is by-and-large the same as ever.
Super Ninja Megaman?
Admittedly, several of the games in the series have added minute changes to the battle engine, but the difference between the Style and Soul Unison systems is honestly negligible at best.
In short, if you really have a deep love and enjoyment for all things Battle Network, you will probably quite enjoy this entry into the saga. If you're tired of three-quarter over-head views and the fetch quest enchantment the series has fallen under, stay way clear.