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 Rank S in acts 12 times.
Found the spring hidden in GREEN HILL Act 1 and reached the goal with a Red Star Ring.
Cleared Sonic Generations.
Executed a trick with a seven-step combo or longer.
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.
Cleared Green Hill within one minute.
Reached the goal without dropping any of the rings you collected in GREEN HILL Act 1.
Got Rank S in an act.
Completed the first stage.
Got Rank S in all acts.
Took no damage while defeating the final boss.
Completed all of Sonic's friends' Challenges.
Chatted with all of Sonic's friends you saved.
Joined the rankings.
Participated in a 30 Second Trial.
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.
Cleared half the missions.
Cleared all the missions.