Garry's mod is a great game, it's so fun building things and experimenting with the different characters, vehicles, weapons, etc. I know people say you need to have a source game, but, I played just fine having only Portal 1 (who's item's aren't even used in gmod) There will be a few missing textures and models from Counterstrike, but it is still very playable and fun with the items provided with the game.

I think that the Binding of Isaac is a really fun game. I've spent a few hours playing it, it's just really fun and addicting. It is very difficult, but dying just makes you want to try again and get farther. Also, it is really fun discovering all of the different types of monsters, exploring the randomely generated rooms, and acquiring cool items. (Which I have rarely seen two of the same)

I definetly recommend this game. One of my favorite I have ever played, and I think it is totally worth my money. There's just so much to do, between doing quests (which is probably a minor part of the game for most people), robbing villagers, riding horses, plundering caverns of zombies. etc.

This game has an awesome open world with hundreds of locations to explore.

You should buy this if you can, especially if it is on sale.