The Intellivision boasted a superior hardware set in comparison to the Atari 2600 at the time. It is considered widely as being the first home gaming console with a 16bit processor inside of it. This gave the unit the ability to better replicate popular arcade titles at home. However, with Atari constantly swooping in and snatching up the major arcade titles, Intellivision relied on many original titles. A good number of which were also released on the VCS, such as Astro Blast, the Tron games, Stellar Conflict, Masters of the Universe, and more.
Mattel managed to sell 3 million units in its life span, up until its discontinuation in 1984. The unit had troubles competing with systems such as the Atari VCS, and ColecoVision. One major push for the unit was the Atari VCS adapter that allowed a gamer to have the best of both worlds without having to invest in both consoles. This helped boost the library considerably.
The Intellivision can still be enjoyed today thanks to AtGames' Flashback unit, even though it is not a true Intellivision under the hood, it still remains very faithful.