https://www.youtube.com/watch?v=eY_YsoR11d8
You might notice that some scenes show more colors onscreen than contemporaries like the C64 - this is all because of the display list interrupt techniques Crawford talks about, combined with clever overlaying of the player/missile sprite system. (The weird term for these hardware sprites is because it's built on the legacy of the 2600's system, which itself was built around the needs of the pack-in games: two players, two projectiles, one ball.)
The A8 series was limited in lifespan in the USA for a number of reasons: poor documentation, platform fragmentation, and price competition. It shipped with very little documentation on how it worked, leaving developers starved for resources for several years(Chris Crawford himself contributed to the unofficial bible, "De Re Atari"). There were the original 8k-upgradeable-to-48k 400/800 models and the newer XL/XE models, which shipped with 64k standard, and additionally, a change partway through the 400 and 800's life to an upgraded graphics chip; although most old software would run on the new machines, the C64 was more straightforward to target and to program, and it led the way in price-cutting the home computer market, which gave it a huge lead in market share. The later life of the A8 was entirely in European markets.
In terms of what the two machines can do when pushed to the limit, though, there's plenty of room for comparison.