You can unlock characters, stages and game modes by completing a certain number of matches. The numbers are pretty accurate. However depending on what game modes you play you might unlock certain things earlier or later.

Tip: If you want to increase your match count really fast try playing Survival Mode with the highest damage setting and the character you can deal the most damage in the shortest time.

Play the number of matches

50 Time Attack
70 Sasuke or beat Story Mode
80 Survival
90 Sasori
100 Wahrehouse Stage
120 Sai
130 Endurance Mode
150 Yamato & Chouji
210 Statviewing
230 Kiba
260 Hinata
290 Shino
300 Difficulty 5
320 Kabuto
350 Orochimarus Lair Stage
400 Tsunade
420 Orochimaru
460 PTS Naruto
490 PTS Sasuke
500 Asuma