a intelligent answer to the 2600
The 8-bit Intellivision featured semi-better graphics than the aging Atari 2600 hardware and it did sell well for the time. Unfortunately for Mattel, they were not able to get recent arcade hits like Space Invaders or Pac Man like Atari did, so they didn't get the attention that the Atari 2600 had (they did get some of those titles but it was too late). One innovation of the Intellivision was the voice module, a device able to produce realistic sound effects and various statements on some of the games (the Odyssey2 had one too).
There was also a Intellivision II out there if anybody remembers it. Plus a INTV System III, which was the Intellivision III under a different company. I don't have anyone of these systems yet so there are no ratings.
Common Intellivision games:
Rare Intellivisions games:
Tower of Doom