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