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