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