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