Here is the full list of all 49 Sonic Generations Collection achievements. It takes around 15-20 hours to unlock all of the achievements on Windows.
Took no damage while defeating the final boss.
Played Time Attack on all stages.
Got Rank S in all acts.
Cleared CHEMICAL PLANT without entering the water.
Got all collectibles.
Got all custom skills.
Got all Red Star Rings.
Chatted with all of Sonic's friends you saved.
Cleared all the missions.
Completed all of Sonic's friends' Challenges.
Cleared Green Hill within one minute.
Got Rank S in acts 12 times.
Found the spring hidden in GREEN HILL Act 1 and reached the goal with a Red Star Ring.
Reached the goal without dropping any of the rings you collected in GREEN HILL Act 1.
Cleared Sonic Generations.
Cleared half the missions.
Joined the rankings.
Participated in a 30 Second Trial.
Got Rank S in acts seven times.
Performed all of Sonic's actions in Act 2.
Executed a trick with a seven-step combo or longer.
Defeated 100 enemies.
Got Rank S in acts three times.
Got Rank S in an act.
Completed the first stage.