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