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 collectibles.
Got all custom skills.
Got all Red Star Rings.
Found the spring hidden in GREEN HILL Act 1 and reached the goal with a Red Star Ring.
Participated in a 30 Second Trial.
Joined the rankings.
Cleared CHEMICAL PLANT without entering the water.
Cleared Sonic Generations.
Got Rank S in all acts.
Chatted with all of Sonic's friends you saved.
Cleared all the missions.
Completed all of Sonic's friends' Challenges.
Got Rank S in acts 12 times.
Executed a trick with a seven-step combo or longer.
Cleared half the missions.
Cleared Green Hill within one minute.
Performed all of Sonic's actions in Act 2.
Got Rank S in acts seven times.
Defeated 100 enemies.
Got Rank S in acts three times.
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.