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.
Cleared CHEMICAL PLANT without entering the water.
Cleared Green Hill within one minute.
Got Rank S in all acts.
Got all collectibles.
Got all custom skills.
Got all Red Star Rings.
Cleared all the missions.
Completed all of Sonic's friends' Challenges.
Cleared Sonic Generations.
Chatted with all of Sonic's friends you saved.
Got Rank S in acts 12 times.
Cleared half the missions.
Got Rank S in acts seven times.
Performed all of Sonic's actions in Act 2.
Found the spring hidden in GREEN HILL Act 1 and reached the goal with a Red Star Ring.
Executed a trick with a seven-step combo or longer.
Defeated 100 enemies.
Participated in a 30 Second Trial.
Joined the rankings.
Got Rank S in acts three times.
Got Rank S in an act.
Completed the first stage.
Reached the goal without dropping any of the rings you collected in GREEN HILL Act 1.