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