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