There's no question in my mind, the Carbine was a very good close range combat weapon. Light, low recoil, 15 shots, and about the power of a .357 magnum put the guys using them at an advantage over the enemy a lot of the time.
But not all the time. For all the stories about how good the carbine was, there are those that tell of it not being as good. Usually its a situational thing, and sometimes its more BS than truth.
One of the stories I heard as a youth came from a neighbor who had been a CB in the pacific. Some island which had been "cleared", his dozer crew was building an airstrip when they got pinned down by a sniper in the treetops. They had carbines, and couldn't get him, the sniper would shoot, then scoot around the backside of the tree, and the carbines just couldn't get through.
This went on for a while, and neither side actually hit anyone, but they knew it was a matter of time before the sniper (who was hitting pretty close) got lucky. At this point they are hunkered down behind the dozer, wondering what to do next and along comes a Marine, a "tall, lanky Texan with a wad of chew in his cheek" and a BAR. "Y'all got a problem, fellahs?"
P'ting goes a round off the dozer
Up comes the BAR, and the Marine "dumps about half a clip of AP" into the treetop.
Sniper rifle falls to the ground, sniper falls to the end of his rope. problem solved.
(or that's the way he told it, anyway
)
Another story came from a friend of mine who had been a commo wireman in Korea. He hated the M1 Garand, and loved the carbine, and gladly admitted he had been fortunate enough to never have had to use either against anyone.
his "hatred & love" came from having to carry them. In the summer, (and per TO&E) he carried a carbine while stringing wire. But, when winter came, they "took away my carbine and made me pack that monster" M1 Garand. This was due to the widespread (and largely false) belief that the carbine wouldn't reliably penetrate the heavy quilted overcoat of the Chinese troops.
There's all kinds of stories out there, good and bad. A lot of them are the typical soldier's tale, if it worked, it was the greatest thing on earth, and if it didn't it was a POS, etc., and these things do grow in the telling...
Even still today, there is no one gun that is the best for every possible situation. The mix of pistol, SMG, carbine, rifle, and BAR (LMG) that the US used during the later half of WWII worked pretty well, usually, (backed up by heavier weapons on call) .
I've spoken to a couple of Germans, who faced that, and they were very impressed by the M1 Carbine (among other things). They said they "loved it" when they could capture one and enough ammo to be useful, because they were "very useful".