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