Word for "easy to dismiss"

Solution 1:

Trivial — ODO

adjective 1. Of little value or importance
"huge fines were imposed for trivial offences"

"Trivial" would satisfy your sentence. Keep in mind the difference between something seeming trivial and actually being trivial.

Solution 2:

His criticism is inconsequential.

Inconsequential

: of no significance : unimportant

"Inconsequential." Merriam-Webster.com. Merriam-Webster, n.d. Web. 28 June 2016.

Solution 3:

You can say

His criticism is negligible.

Collins says that

An amount or effect that is negligible is so small that it is not worth considering or worrying about.

• e.g. The cost is huge, the effect negligible. (Times, Sunday Times, 2011)

Solution 4:

"His criticism was uncalled for." "His criticism is superfluous."

Or with feeling, "His criticism aggravated me."

Or on the slang side. "His criticism sucked"