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.
Cleared CHEMICAL PLANT without entering the water.
Took no damage while defeating the final boss.
Played Time Attack on all stages.
Cleared all the missions.
Completed all of Sonic's friends' Challenges.
Cleared half the missions.
Got Rank S in all acts.
Cleared Green Hill within one minute.
Cleared Sonic Generations.
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.
Got Rank S in acts seven times.
Participated in a 30 Second Trial.
Joined the rankings.
Got Rank S in acts three times.
Executed a trick with a seven-step combo or longer.
Defeated 100 enemies.
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.
Got Rank S in an act.
Completed the first stage.