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