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