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.
Cleared CHEMICAL PLANT without entering the water.
Got all custom skills.
Cleared Sonic Generations.
Got all collectibles.
Cleared all the missions.
Completed all of Sonic's friends' Challenges.
Chatted with all of Sonic's friends you saved.
Got all Red Star Rings.
Got Rank S in all acts.
Cleared half the missions.
Got Rank S in acts 12 times.
Got Rank S in acts seven times.
Performed all of Sonic's actions in Act 2.
Cleared Green Hill within one minute.
Participated in a 30 Second Trial.
Got Rank S in acts three times.
Found the spring hidden in GREEN HILL Act 1 and reached the goal with a Red Star Ring.
Executed a trick with a seven-step combo or longer.
Got Rank S in an act.
Completed the first stage.
Reached the goal without dropping any of the rings you collected in GREEN HILL Act 1.
Joined the rankings.
Defeated 100 enemies.