It's a tricky balance but I think the safest bet is to look at other games in your genre and price bracket and see how long their gameplay is, if you can. People will naturally compare your games to others so it's good to know how yours stacks up anyway.
One very specific example of group failure is Hero6. They were around for many years but they never finished their game, despite people's best intentions. They accepted members from all over the place and they all lost interest over time.
You mentioned in two posts now that you'd like to make flash games. Do it! I know some C++ and ActionScript. I think you will appreciate Flash and ActionScript because the results are more immediate, so your learning is rewarded faster.
That said, you don't need to be committed to it to the bitter end. Focus on it for a few weeks and you'll know if it's for you. C++ has more options as far as engines and libraries you can use it with (I use a 3D engine called Leadwerks) but as people have said, there are no wrong choices to start learning.
there is no game engine that requires no programing
Not true. For example, Construct 2 requires no coding and you can get a playable game going with it (though it's a 2D engine). There is also scripting, which tends to be simpler than coding, which many engines support. That said, I don't have an answer for you. I personally use Leadwerks, which is simple C coding.
Now i'm trying to make Arkanoid, Breakout clone. But I don't know how to do things, what classes I should write, how every class interacts with each other. How to handle maps. And I need to learn some math about vectors and stuff. But I can't find a book or tutorial that covers it all... I can find books but they are written for 3D games, and 3D maths. I don't know what to do. I'm REALLY lost...
I would like to hear how YOU learned to program games. What did you read, what tutorials have you read/watched? And how much math do I really need to learn.
I haven't read the other responses but:
For a Breaktout and Arkanoid clone, you don't need vectors. You can work just with x and y and their respective velocities. Will being comfortable with vectors help? Sure.
I learned very early on (many years ago) by copying code from books and then modifying them. Today, this is equivalent to taking examples from SFML and changing them around. Or take pieces you want from each. It's really just a matter of practice and experimentation.
Finally, being on forums is a great thing. Posting "stupid" questions here and other forums helped me a lot because there are some nice people out there. When you can, try to reciprocate and help others in turn. You'll still learn things too and people will appreciate it as much as you did.
What was the idea I don't remember my first few but the one I do remember was called Dagger. The idea was simply to run around in an top-down RPG world throwing daggers at monsters, killing them.
How far did you get with it The game had the main character sliding around (because he wasn't animated) and throwing daggers at purple blobs, which simply disappeared when killed. I think I had a version where the blobs popped in a very satisfying 3-frame animation. I forget if it had health or death for the main player. Pretty sure it didn't though.
How did that game idea evolve as it transitioned into reality or fell short of being completed The goal was to have multiple levels with varying amounts and types of monsters but I kept the idea suprisingly modest, for what little that helped. There was going to be a few powerups and I think dagger pickups, as the throwing daggers were going to be limited, I think.
What lessons did you learn on the way Keep things simple because even "simple" games are harder than they seem. And that my skills were far below the needed skills to implement my dreams.
What would the game be, if you revisited the original idea now and built the game with your current ability/knowledge I actually restarted this game in 3D (with Leadwerks). It's much easier now than so many years ago, when one of my greatest headaches was how to display 2D trees, enemies and monsters in the right order so they display correctly.
3DS Max for 3D Photoshop for more "realistic" graphics and textures, and also for 2D sprites and tiles GraphicsGale also for 2D sprites and tiles. It's free and it also does animations on separate layers.