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.
Got all custom skills.
Got all Red Star Rings.
Played Time Attack on all stages.
Cleared all the missions.
Completed all of Sonic's friends' Challenges.
Got Rank S in all acts.
Cleared CHEMICAL PLANT without entering the water.
Cleared Green Hill within one minute.
Took no damage while defeating the final boss.
Reached the goal without dropping any of the rings you collected in GREEN HILL Act 1.
Cleared half the missions.
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 Sonic Generations.
Participated in a 30 Second Trial.
Chatted with all of Sonic's friends you saved.
Performed all of Sonic's actions in Act 2.
Joined the rankings.
Got Rank S in acts seven times.
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.