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