Sharing achievements accross Google Play games
Can Google Play achievements be shared between two different Google Play games? For example if a user unlocks some achievements on Street Brawler 1 game, can he keep those achievements and see them on his new Street Brawler 2 Google Play game?
No, you can't do it. Achievements are associated to a particular application through the package name. If you publish a new game this one should have a different package name to be published in the market and therefore you will need to register and associate a new achievements list. However, it's totally possible to implement a migration/adapter system so you can have the achievements of the first game in the second game, but you know... you have to implement it by hand.
That's not exactly true, you can add up to 20 games (link 20 package names) to one google play service, all sharing the same achivements and leaderboards. This is basically created to use the same achievements in the same game on multiple platforms, but you can also use it with totally different games.
You can add Street Brawler 1 and 2 (link them under google play services), use the same achievements ids in both games, and they will share the same achievements. If you got them in Street Brawler 1 you will have them in Street Brawler 2.