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