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