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