Accomplish the indicated achievement to get the corresponding number of Gamerscore points:

2 TD Kickoff Returns in a game (75 points): Return 2 Kickoffs for a TD in a game (non co-op).
Shut out Rival in a Franchise (50 points): Shut out Rival in a Franchise game (non co-op).
Kick a FG for over 50 yards (15 points): Kick a FG for over 50 yards in a Franchise game (non co-op).
Complete a game without an INT (30 points): Complete a game without an interception, 5 min+ quarter length (non co-op).
6 Rush TDs with the Dolphins (50 points): 6 Rush TDs in a game with the Dolphins (non co-op).
Catch 10 passes in a game (50 points): Catch 10 passes in a game with one receiver (non co-op).
Complete game without fumbling (25 points): Complete a game without fumbling, 5 min+ quarter length (non co-op).
2 TD Punt Returns in a game (65 points): 2 TD Punt Returns in a game (non co-op).
Intercept 6 passes in a game (50 points): Intercept 6 passes in a game (non co-op).
Hold a Rival to under 300 yards (50 points): Hold a Rival to under 300 yards total offense in a game (non co-op).
Score 60 points in a Rival game (30 points): Score 60 points in a Rival game (non co-op).
Score 40 points in a Rival game (20 points): Score 40 points in a Rival game (non co-op).
Record 12 sacks in a game (50 points): Record 12 sacks in a game (non co-op).
6 sacks with 1 player in a game (50 points): 6 sacks with 1 player in a game (non co-op).
80% completion for a game (50 points): 80% pass completion in a Franchise game, 5 min+ quarter length (non co-op).
7 Pass TDs with the Falcons (50 points): Throw 7 pass TDs in a game with the Falcons (non co-op).
550 Pass Yds with the Titans (50 points): 550 Pass Yds in a game with the Titans (non co-op).
300 Rush Yds with the Jets (10 points): 300 Rush Yds in a game with the Jets (non co-op).
Hold a Rival to under 20 points (10 points): Hold a Rival team to under 20 points in a game (non co-op).
Midway Monster (50 points): Create a legendary player from the past.
Can You Believe These Seats?! (30 points): Celebrate a touchdown in a wall hotspot.
Steal Their Thunder (30 points): Steal an opposing player's touchdown celebration.
Slam Dunk All-Star (30 points): Dunk the ball over the goalpost (or at least attempt to) after a touchdown.
Shine In The Spotlight (30 points): Celebrate a touchdown in an endzone hotspot.

Additionally, there is one secret achievement:

Now Here's A Guy (50 points): "Thanks for buying Madden NFL 09. Here's to another 20 years." Create a player named "John Madden" and assign him to any team.