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.
Cleared Sonic Generations.
Got all collectibles.
Cleared all the missions.
Completed all of Sonic's friends' Challenges.
Got all Red Star Rings.
Got Rank S in all acts.
Chatted with all of Sonic's friends you saved.
Cleared CHEMICAL PLANT without entering the water.
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.
Executed a trick with a seven-step combo or longer.
Cleared Green Hill within one minute.
Joined the rankings.
Participated in a 30 Second Trial.
Got Rank S in acts three times.
Defeated 100 enemies.
Reached the goal without dropping any of the rings you collected in GREEN HILL Act 1.
Found the spring hidden in GREEN HILL Act 1 and reached the goal with a Red Star Ring.
Got Rank S in an act.
Completed the first stage.