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