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