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.
Cleared Green Hill within one minute.
Got all custom skills.
Got all collectibles.
Cleared all the missions.
Completed all of Sonic's friends' Challenges.
Got all Red Star Rings.
Cleared half the missions.
Cleared Sonic Generations.
Took no damage while defeating the final boss.
Got Rank S in all acts.
Chatted with all of Sonic's friends you saved.
Performed all of Sonic's actions in Act 2.
Got Rank S in acts 12 times.
Got Rank S in acts seven times.
Cleared CHEMICAL PLANT without entering the water.
Executed a trick with a seven-step combo or longer.
Participated in a 30 Second Trial.
Reached the goal without dropping any of the rings you collected in GREEN HILL Act 1.
Joined the rankings.
Found the spring hidden in GREEN HILL Act 1 and reached the goal with a Red Star Ring.
Got Rank S in acts three times.
Defeated 100 enemies.
Got Rank S in an act.
Completed the first stage.