Here is the full list of all 37 Eragon achievements worth 1,000 gamerscore. It takes around 8-10 hours to unlock all of the achievements on Xbox 360.
You have made it through the FINAL BATTLE on HARD.
You have made it through the FINAL BATTLE on NORMAL.
You have collected all the secret eggs
You have beaten the DEFEND THE VARDEN level on HARD.
You have beaten the DEFEND THE VARDEN level on NORMAL.
You have beaten the URGAL ATTACK! level on NORMAL.
You have beaten the URGAL ATTACK! level on HARD.
You have made it through the MISTY GORGE level on HARD.
You have made it through the MISTY GORGE level on NORMAL.
You have made it through the URGAL ENCAMPMENT level on NORMAL.
You have made it through the URGAL ENCAMPMENT level on HARD.
You have made it through the BEOR MOUNTAINS level on HARD.
You have made it through the BEOR MOUNTAINS level on NORMAL.
You have beaten the RUINS OF ORTHÍAD level on HARD.
You have beaten the RUINS OF ORTHÍAD level on NORMAL.
You have beaten the FLIGHT FROM GIL'EAD level on NORMAL.
You have beaten the FLIGHT FROM GIL'EAD level on HARD.
You have made it through the DURZA'S FORTRESS level on HARD.
You have made it through the DURZA'S FORTRESS level on NORMAL.
You have made it through the GIL'EAD KEEP level on NORMAL.
You have made it through the GIL'EAD KEEP level on HARD.
You have made it through the GIL'EAD CITY level on HARD.
You have made it through the GIL'EAD CITY level on NORMAL.
You have beaten the TRAPPED! level on HARD.
You have beaten the TRAPPED! level on Normal.
You have beaten the RA'ZAC CHASE level on NORMAL.
You have beaten the RA'ZAC CHASE level on HARD.
You have made it through the DARET BRIDGE level on HARD.
You have made it through the DARET BRIDGE level on NORMAL.
You have made it through the DARET TOWN level on NORMAL.
You have made it through the DARET TOWN level on HARD.
You have made it through the DARET DOCKS level on HARD.
You have made it through the DARET DOCKS level on NORMAL.
You have made it through the CARVAHALL level on HARD.
You have made it through the CARVAHALL level on NORMAL.
You have made it through the SPINE MOUNTAINS level on HARD.
You have made it through the SPINE MOUNTAINS level on NORMAL.