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