The game's frame rate is tied to the BGM engine. When music plays, the game frequently lags or drops frames on modern Windows versions.
You can expect roughly 12 hours for a main story run, but completionists can spend over 45 hours unlocking all costumes and gallery items.
For a deep dive into the game's mechanics or to find community fixes, the Devil May Cry Wiki is an excellent resource for performance tips.
during a Steam sale. It frequently drops to a very low price and provides a much safer, smoother experience than the 2006 cracked version.