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