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.
Played Time Attack on all stages.
Took no damage while defeating the final boss.
Got Rank S in all acts.
Got all collectibles.
Got all custom skills.
Got all Red Star Rings.
Cleared CHEMICAL PLANT without entering the water.
Cleared Green Hill within one minute.
Performed all of Sonic's actions in Act 2.
Got Rank S in acts 12 times.
Got Rank S in acts seven times.
Participated in a 30 Second Trial.
Joined the rankings.
Chatted with all of Sonic's friends you saved.
Cleared all the missions.
Completed all of Sonic's friends' Challenges.
Cleared half the missions.
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.
Executed a trick with a seven-step combo or longer.
Got Rank S in acts three times.
Defeated 100 enemies.
Got Rank S in an act.
Completed the first stage.