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