1. I don't play computer games much.

2. I don't play computer games a lot.
3. I don't play computer games more than my brother.
4. I don't play computer games as much as my brother.
5. I don't play computer games less than my brother.
6. I play computer games more than my brother.
7. I play computer games as little as my brother.
8. I don't play computer games as little as my brother.
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Q1: Would you check the sentences?
Are they all grammatical?
Q2: Which one is right, #1 or #2? Are both OK?

#s 1 and 2 are fine as they are.

I'd use these replacements:

3. I don't play computer games more than my brother does.

4. I don't play computer games as much as my brother does.

5. I play computer games as much as my brother does.

6. I play computer games more than my brother does.

7. I play computer games less often than my brother does.

8. (See #3.)

If you don't have "does" at the ends of those sentences, then it's not clear if you mean playing computer games or playing your brother!

Q1: Let's check the sentences for their grammaticality.

1. "I don't play computer games much." - This sentence is grammatically correct.

2. "I don't play computer games a lot." - This sentence is also grammatically correct.

3. "I don't play computer games more than my brother." - This sentence is grammatically correct.

4. "I don't play computer games as much as my brother." - This sentence is grammatically correct.

5. "I don't play computer games less than my brother." - This sentence is not grammatically correct. Instead, you could say, "I play computer games as much as my brother."

6. "I play computer games more than my brother." - This sentence is grammatically correct.

7. "I play computer games as little as my brother." - This sentence is grammatically correct.

8. "I don't play computer games as little as my brother." - This sentence is also grammatically correct.

Q2: Both #1, "I don't play computer games much," and #2, "I don't play computer games a lot," are correct and can be used interchangeably. They both convey the same meaning, indicating that the speaker does not engage in computer games frequently.