In my humble opinion, The Message is a good translation to read. Like Good News. When studying, it is obviously not a good translation. Some folks are such KJV fans that they will not read other translations and believe them to be inferior, when in point of fact biblical scholarship has advanced greatly since 1611, and so other translations are very accurate, more so than KJV.
Some other folks are so set on using their own translation that The Message meets with disapproval simply because it is not a word for word rendering of the original Greek. Having looked into The Message and Eugene Peterson, I have heard The Message quoted on several national radio and tv ministries, by pastors who are very very biblical indeed.
It is not a dumbing-down of the Bible, it is written in the same everyday language as the original Greek text, which itself was not formal. People think that a text must be formal if it talks about God. Jesus did not speak in a formal way. He told down-home parables about mustard seeds and wheat, not the latest theological dogma out of the OT, so if speaking naturally was good enough for Jesus while He was on this Earth, then a plain ol text of what happened with his ministry is good enough for us. Not for study purposes, but certainly for reading.
The idea is to make Bible reading easier for those who would not crack open a Bible the way some translations read, in such a formal way. I had a friend recently who was diagnosed with cancer. A friend said to read the book of Job. She had a great deal of difficulty understanding it and was quite despondent. I told her, look, there is a plain English translation, not superior to others but plain nevertheless, I will order it from amazon for you and you can delve into Job THAT way and now she has read Job and understands it. So if understanding the text of the OT and NT is the goal, then The Message fills that niche very nicely. If you look for more serious and more accurate word for word, then The Message is not good for that.
Now, it should go without saying, that all this is just my humble opinion, and I mean humble, so to write and dispute this or that is all to no avail, as I am voicing opinions only, which are not really subject to scrutiny, thankfully, as they do not pretend to be authoritative

An opinion is never authoritative.