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