One of the most important things that's constantly told to any developer over and over again is how important the end user is. You have to have consideration for the player. What is that though really? It's more than just knowing your target audience and developing accordingly.
Small file sizes aren't just for improved performance, they will also make your players happy that the game isn't eating their hard drive space. If you're making a game for pc. If it's on a disc, most devs tend to not worry as long as it fits. This then can result in some problems when doing a pc port later or if consideration isn't taken for the pc players if you're developing for both. By problems of course I really just am complaining about the obscene size of some games that clearly weren't a thought for devs when they did a pc port. Though they can also seriously alter performance and load times as well. So this is one thing to consider.
Interface is another, not just GUI but the basics as well. Knowing if it's a controller or keyboard and mouse, and giving more user control over these things. Namely the option to turn off or modify controller key maps on pc, and change keys on the consoles would be nice. Not everybody is going to like how you choose to implement these interface methods and will undoubtedly want to do it their way and it's not that hard or unreasonable to accommodate them.
Understanding the value of the player's time and cutting out unnecessary grinding just to lengthen playtime. It doesn't make your game good and it's not about to convince me to buy a sequel. Games like ICO or Shadow of the Colossus are great examples of how to either completely cut out the grind, or disguise the grind so well you have absolutely no idea it's going on. In the later example grinding is also entirely optional. Don't even try to argue that the series of boss fights is somehow a grind in itself because while vaguely repetitious each fight is notably different and doesn't meet the requirements to actually be called grind. Keep in mind grind is not repetition in and of itself, it's repetitive tasks that don't forward a plot or have minimal rewards. For example in games like runescape where you can mine ore for days to make a few sets of armor to sell for coin. That is grindtastic.
This isn't meant to be a rant. More precisely I'm pointing out that a good game merely takes consideration of it's players in as many aspects as you can conceive. Try to think about it as though you were already playing, and would you really want to go through that process as a player.