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