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.
Participated in a 30 Second Trial.
Joined the rankings.
Got Rank S in all acts.
Got all collectibles.
Took no damage while defeating the final boss.
Got all custom skills.
Cleared Sonic Generations.
Cleared all the missions.
Completed all of Sonic's friends' Challenges.
Chatted with all of Sonic's friends you saved.
Got all Red Star Rings.
Cleared CHEMICAL PLANT without entering the water.
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.
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 acts three times.
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.