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