Here is the full list of all 49 Sonic Generations Collection achievements. It takes around 20-25 hours to unlock all of the achievements on Windows.
Played Time Attack on all stages.
Got all collectibles.
Participated in a 30 Second Trial.
Joined the rankings.
Got all custom skills.
Got all Red Star Rings.
Cleared CHEMICAL PLANT without entering the water.
Cleared all the missions.
Completed all of Sonic's friends' Challenges.
Took no damage while defeating the final boss.
Cleared Sonic Generations.
Got Rank S in all acts.
Chatted with all of Sonic's friends you saved.
Cleared half the missions.
Cleared Green Hill within one minute.
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 12 times.
Performed all of Sonic's actions in Act 2.
Got Rank S in acts seven times.
Executed a trick with a seven-step combo or longer.
Defeated 100 enemies.
Got Rank S in acts three times.
Got Rank S in an act.
Completed the first stage.