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.
Joined the rankings.
Participated in a 30 Second Trial.
Chatted with all of Sonic's friends you saved.
Got all collectibles.
Got all custom skills.
Got all Red Star Rings.
Cleared Green Hill within one minute.
Cleared Sonic Generations.
Cleared all the missions.
Completed all of Sonic's friends' Challenges.
Got Rank S in all acts.
Cleared half the missions.
Got Rank S in acts 12 times.
Got Rank S in acts seven times.
Performed all of Sonic's actions in Act 2.
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.
Reached the goal without dropping any of the rings you collected in GREEN HILL Act 1.
Defeated 100 enemies.
Got Rank S in acts three times.
Executed a trick with a seven-step combo or longer.
Got Rank S in an act.
Completed the first stage.