How many levels does each game usually have

It's a common misunderstanding that videogames are simply level based. However you may think of games from previous generations, where a basic side-rollers and other genres where level oriented. In this case your answer is from 3 to 15. The classic Tetris has 30 "levels". A modern "level-based" game like Call of Duty 4 has several "levels" within 4-5 Acts.