A lot of people think that unlimited fricking bullets are the solution, but what you really need is few bullets but big bullets, this was my Ted talk
It depends on what type of game you have. A more action-packed one would have a ton of small bullets with a high fire rate while a more strategic game would have a few really big bullets with a low fire rate.
They would also have good controls, a very indistinguishable player character and a lot of weapons
I think having two or more bullet styles, and some enemies with different types of shooting it's also appreciated
