This is technically a second-hand review.  I was all set to write up my own review, but then I found someone else had already said exactly what I was planning to say.

So you can just read this review from the site GrubGrade instead.

The key points:

These M&M’s do a so-so job of replicating the frosted chocolate birthday cake flavor and not enough to really impress me.  Birthday Cake M&M’s taste way too much like regular milk chocolate M&M’s to be memorable.

I wish the Mars company went with a yellow cake, white frosting birthday cake flavor instead of milk chocolate.  Even though I have a personal bias against chocolate birthday cake, I still think these M&M’s tasted too much like the traditional M&M’s for me.  Regular M&M’s are still great, a classic, so these are by no means bad… just no wow factor.

That perfectly echoes my sentiments, right down for me not being a big fan of chocolate birthday cake.