Here is the full list of all 49 Sonic Generations Collection achievements. It takes around 20-25 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.
Cleared CHEMICAL PLANT without entering the water.
Cleared all the missions.
Completed all of Sonic's friends' Challenges.
Got Rank S in all acts.
Got Rank S in acts 12 times.
Played Time Attack on all stages.
Got Rank S in acts seven times.
Cleared Sonic Generations.
Chatted with all of Sonic's friends you saved.
Found the spring hidden in GREEN HILL Act 1 and reached the goal with a Red Star Ring.
Cleared Green Hill within one minute.
Executed a trick with a seven-step combo or longer.
Cleared half the missions.
Performed all of Sonic's actions in Act 2.
Got Rank S in acts three times.
Joined the rankings.
Reached the goal without dropping any of the rings you collected in GREEN HILL Act 1.
Participated in a 30 Second Trial.
Defeated 100 enemies.
Got Rank S in an act.
Completed the first stage.