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.
Cleared all the missions.
Played Time Attack on all stages.
Completed all of Sonic's friends' Challenges.
Got all custom skills.
Got all Red Star Rings.
Took no damage while defeating the final boss.
Participated in a 30 Second Trial.
Joined the rankings.
Got Rank S in all acts.
Cleared Sonic Generations.
Chatted with all of Sonic's friends you saved.
Cleared CHEMICAL PLANT without entering the water.
Cleared Green Hill within one minute.
Cleared half the missions.
Got Rank S in acts 12 times.
Got Rank S in acts seven times.
Performed all of Sonic's actions in Act 2.
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.
Defeated 100 enemies.
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.