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