That's the spirit! Just because you have grand dreams, doesn't mean you can't pull 'em off.
If you've never made a game, try starting with the smallest project imagineable. Create a game like Pong or Asteroids. Even this could take a lot of time for new developers. Once you have something basic working, try to polish it. Add high scores, menus, options. These small pieces will all be valuable learning experiences.
Any game with multiple mechanics is a rough place to start. Diablo 1 might look simple but it's really several mini-games in one. There's the combat part, the loot part, the dialog part, the inventory part, etc. Each of those might be more complex to make than an entire game of Pong.
Start small and grow from there
I always encourage people to implement the smallest vertical slice of gameplay possible. E.g. one level, one enemy, no menus. If it's fun enough you'll be motivated to continue working on it and add more features incrementally. Plus, having something playable early is nice to show off to friends and fans.
If you can't get the core gameplay fun, you'll find out quickly. Take what you've learned and try something new.
The Second 90%
"The first 90 percent of the code accounts for the first 90 percent of the development time. The remaining 10 percent of the code accounts for the other 90 percent of the development time." -Tom Cargill, Bell Labs
It's one thing to make a game playable; it's another thing entirely to polish and ship it. This is hard to plan for but you'll get better with every game you finish. Another good reason to start small and work your way up.
Not an artist? There are collections of game art with permissive licenses. My favorite is Open Game Art which features plenty of Creative Commons works.
Here's a great collection of indie resources, everything from music to marketing info.