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.
Cleared all the missions.
Played Time Attack on all stages.
Got all custom skills.
Completed all of Sonic's friends' Challenges.
Cleared half the missions.
Got all Red Star Rings.
Chatted with all of Sonic's friends you saved.
Cleared Sonic Generations.
Took no damage while defeating the final boss.
Got Rank S in all acts.
Got Rank S in acts 12 times.
Performed all of Sonic's actions in Act 2.
Got Rank S in acts seven times.
Found the spring hidden in GREEN HILL Act 1 and reached the goal with a Red Star Ring.
Defeated 100 enemies.
Cleared CHEMICAL PLANT without entering the water.
Got Rank S in acts three times.
Joined the rankings.
Cleared Green Hill within one minute.
Executed a trick with a seven-step combo or longer.
Participated in a 30 Second Trial.
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.