[Jotaku]

Well, if you simply google "best anime games", all you see are mass articles about best anime games with their own opinions. 
We have absolutely zero idea if they are biased, or even paid to advertise particular games by some video game companies for their own marketing purpose and so on.
Also you can't simply determine the best anime games by just a number of sells, as selling can differ by how much marketing effort are made. That means it may be still manipulated by capital. In other words, when determining quality, a large amount of evaluations by random end users is more important to consider than other factors.

If you're looking for a truly unbiased best anime game that embraces everyone's opinion, you have no choice but to vote. Of course, even that vote can be unfair enough if anyone can vote multiple times. So the vote should allow only one vote per a person.

Such votes for the best anime games can be found on Anime Esports. One another great thing is that you can also view the replies of voters providing why they have voted for their best anime games, but not all of them as not everyone want to write a long description of their opinions right

As of this writing, on June 23, 2021, following 5 anime games are the best:
Sword Art Online: Fatal Bullet
17 score, 22.08%

Genshin Impact
7 score, 9.09%

Kandagawa Jet Girls
6 score, 7.79%

Code Vein
5 score, 6.49%

Senran Kagura: Peach Beach Splash

5 score, 6.49%

The new anime game "Scarlet Nexus" has recently been added, so we won't know if the ranks would change.
I am entirely sure this ranking will be changed though in the future. Please visit that page to be up-to-date.

Also please make sure, you can also always participate in voting, and leave your own reason why your particular anime games are the best.
Hope this helps you.