These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
On the one hand, it's pretty much a downer for Charlie - soon after he truly discovers his family roots and realizes his and Raymond's history together, he has to return him to Wallbrook. And Raymond obviously benefited from being outside in the "real world" for a while.
On the other hand, it's also obvious that Raymond's ability to grow is severely limited by his disability, and he is utterly incapable of dealing, in the long run, with the vicissitudes of the Real World. It worked out best for both of them - Charlie had the freedom to continue his life, and Raymond had the safety and 24/7 care of the institution. Charlie could come back and visit at any time (and probably did).
Glurge: Despite the general positivereception of the movie and awesome acting on the part of Dustin Hoffman, for many autistic people, the movie's much more Glurge then anything else. The simplistic portrayal of autism in the movie, and the way it's used as a plot device to teach the "neurotypical" protagonist not to be a Jerk Ass, make it guaranteed Flame Bait on many autistic support forums.
So Okay, It's Average: Perhaps due to Autism being better-known these days, some people find the movie pretty unremarkable despite the hype.