As a gaming machine it's superior to the Apple 2, but Apple had more games.
As a gaming machine it usually falls short of the C64, but it does have a faster CPU which gives it an advantage in rare cases. I think it also has a better floppy drive, people hate C64 floppy drives.
Most game boxes back then used screenshots from the C64 version because it looked the best. You had to guess what your version would look like.
The A8 was dropped by game developers sooner than Apple or C64, so some games that appear on the latter don't appear on the A8. One factor in that may have been piracy - people figured out some exploit for Atari floppy drives that allowed making perfect copies, and game publishers weren't happy about it.
I'm sure the general instability of Atari (the company) didn't help either, and I think their system sales dropped off sooner than C64 or A2.
The 2600 wasn't expected to stay on the market long. The hardware in the Atari 400/800/etc was meant for a next-gen console which would quickly replace the 2600. The graphics and sound are much improved. It can play music on-key, it can display more moving objects without flicker and can display text properly. It surely would have had much more RAM allowing more complex games. The 2600 doesn't even have a dedicated RAM chip, just the 128 bytes that's built into an IO chip they were using.
The guy who started Atari (Nolan Bushnell) sold the company to Warner, then feuded with them over his plan to replace the 2600. Warner saw it's sales ramping up and didn't want to mess with it, Bushnell wanted to stay ahead of competitors and "wow" people a little more. That A8 hardware got released as a computer instead. The 2600 boomed but became obsolete while Warner kept milking it. The A8 hardware did eventually get consolized in the Atari 5200, but that was years later and it was ruined by bad controllers.
It was hard to make games with much depth on the 2600. It really only lent itself to simple genres, and this combined with the glaringly obsolete looking graphics were IMO major reasons people got burned out on Atari and dismissed video games as a dying fad.
I didn't have an A8 back then, but when I discovered them on AtariAge I got interested. I love the idea of a PC with a cartridge slot. I bought an 800XL a year ago but due to a keyboard issue I haven't used it much.
One game I do prefer on the 2600 is Space Invaders. That version is a masterpiece, the A8 version looks and feels wrong to me.
I don't have Star Raiders but from what I understand it's much better on the A8, the 2600 is too limited to do it very well.
Donkey Kong on the A8 is many people's favorite home version, I haven't played it myself, I just know it has a good reputation. They did reformat the level layout to fit a horizontal 4:3 television, but it has all the stages and people seem to like how it plays.