There are currently no very demanding games. This is mostly due to poor optimization. But if the game is well optimized and it still dulls, lags, freezes, then most likely the problem is in your device.
République previously played it, possibly demanding, as the weight of the game is appropriate (about 6GB). The game itself is similar in style to the computer Wotch Dogs.
I think there are no most demanding games. You can choose games to your taste, what you like my game personally Zooba I play it and I'm fine. But if the lag is not my fault, personally, everything is fine.
There are quite a few very demanding games on Android right now. Often these are online projects that are very demanding on hardware and network quality.
In my subjective opinion, this is:
This is not a complete list, I think there are many more. But the fact that they are very demanding is for sure, since the developers are not able to optimize the game for each particular gadget. Therefore, for a comfortable game in such heavy projects you need good hardware.
If you want to learn more about these and other games, I advise you to study the list here.