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