If you are still looking to try out GTA 4 on Steam, you might have to scrap that plan now as it was announced that the game is no longer available to purchase on Steam.
A ResertEra forum discovered that the game no longer has a purchase button on Steam. The page did not explain why this is happening to GTA 4 and we have not heard from Rockstar Games as well.
Some people have started speculating that it might have something to do with the music licensing while others think that it might be Rockstar looking to move the game over to their own Rockstar Launcher.
While GTA 4 is no longer available, there is still GTA 5 and San Andreas on Steam so you can try those out first while we see where GTA 4 will go.