2.) Along the same lines, the game needs to feel COMPLETE. I ran out of time and didn't quite get to all I wanted, and that did hurt me I think.
This is the reason Duke is rather short. I spend so much time trying to create the controls that I was running out of time to finish the game. I decided I wanted my game to rather be short but finished than long but unfinished, and spend the final hours making the ending sequence so the game would feel complete. Downside is, the game is very short and doesn't properly show all the cool stuff you can do with dashing, the upside is, the game is simple and short enough that most people have the patience to play through it.
3.) Being unique and innovative is nice, but ultimately your game just needs to be fun. If you can accomplish that with a simpler, more generic concept, than go for it (AdventureIslands stuck to his platforming guns, and look where he landed!). Whatever concept it is, just make it the best it can be.
I tried my hardest to NOT create yet another platformer, but failing that I wanted to give the game at least an unique twist, to make something different and new instead of "just platformer." I came up with the Dash mechanic and end result turned out pretty well. Bit clunky in compo entry, but I've already made the controls smoother for upcoming post-compo version.
But I agree, the most important thing is that the game is fun to play. If your game is not fun, nobody's gonna stick around to play it, or rate it properly.
Ludum Dare is more about developing your game dev skills rather than being #1, and I think it's a more important skill as a game developer to make new and creative games rather than pandering to the masses by making something safe and reliable.
This. Every LD I try making something different. My games have mostly been platformers, but at least they all have something different and new to them. In Persist you lost your skills as you continued playing, in Duke you dash around. I keep learning more and more by trying little something new all the time. It can be a huge risk to try something new with such a short time limit, but in the end it can be very rewarding too.