I am wanting to challenge myself to build a simple game, that has a character and a randomly generated world. If I get anywhere with it I may perhaps I'll develop it into something more, but the key challenge I want to tackle is cross-platform. I'd also want to have a go at creating engine myself, doing lighting and other bits.

Is it worth me using a system like Unity or do I go down a more custom route?

The game I would like to make is a 2D game so whether that changes the tools I should use, it would be great to know as well.

Supporting mobiles isn't something I am worried about at moment, just looking for Mac and Windows for time being. In future I'll consider other platforms if I get anywhere with the development.

So if anyone has any recommendations for a language, engine or system to use would love to her your thoughts.Including pros and cons would be helpful and appreciated and if you can do comparisons that would be awesome as well!