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