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