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