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