Entex started out making the simpler, less playable LED sports games like Baseball, Tennis, Football, etc...  Once the arcade game craze really took off, they started producing games based on popular stand-up arcade games of the day like Galaxian, Stargate, and Defender. They were made with a Vacuum Fluorescent Display (VFD), which was far better looking than the more common and cheaper to manufacuture LED displays.  Once established as a quality handheld producer, their boastful marketing claimed: "Games for the discriminating player"!

They also made many of their games better by adding a speed dial, which directly controls the speed of the gameplay.  This allowed gamers to more precisely find a comfortable level of gameplay, as many handhelds were either too easy or too hard.  Another cool thing with the speed dial, is that when adjusted it also lowers or raises the pitch of the sound output, so I guess the sound processing must have been on the same PCB bus as the rest of the game's processing.  I don't know of any other handheld companies that used speed dials besides Entex!  Other nice game features that made them competitive - almost all of their games had sound/mute toggle, a demo startup mode, good quality joystick controls, and very responsive buttons.

Here are the entex games that I have, grouped by display type: