1. Reliability. Leaking or troublesome guns are a definite no go. I buy a gun to enjoy not fix or guess what's wrong with it.
2. LCD screen. Ability to provide immediate user feedback, customization, or change modes. Counting blinking lights etc is garbage. Technology is readily available today to support such options. Let's not continue with infancy of paintball.
3. Performance. with regard to cycle speed and air efficiency to sustain a normal length and volume of fire in a game.
4. Quality of workmanship. Companies out to make a quick buck or produce low quality products will not survive. People don't talk about or loath crappy guns.
5 Innovation. Make something that is groundbreaking or unique that sets your products apart from the competition. (Invert Mini)