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