Limitless the book was much better than Limitless the movie. And, yes, it doesn't have a Hollywood-style happy ending
at all.
I just finished reading "Flowers for Algernon" the short story and I never read the novel. It also immediately reminded me of "Limitless". (The book, I wouldn't compare it to the movie, again, at least because of that silly "happy end", which seems to be obligatory in the Hollywood.) If you want somebody's (i.e. mine) take on it: well, "Limitless" was much, much better of a read. I was a lot younger when I read it, so I don't how I would react now, but I remember it to be pleasantly realistic, unlike the vast majority of [English] sci-fi. Unlike in the movie, though, there was a lot less "magic" to MDT. There was no silly stuff like being suddenly able to multiply 10-digit numbers in the head and similar Hollywood representations of "being incredibly intelligent" which are just annoyingly stupid, if you ask me. In the book it felt very real, it was very easy to "feel" what is that effect. It's basically just an exceptionally potent nootropic drug, think "amphetamine, but better". And, yes, that was motivational. This is the main reason I remembered it, actually: there I very much felt how the protagonist was "improved". In the "Flowers for Argernon", on the other hand, it just feels like author is trying to explore some idea he isn't mentally equipped to explore. I.e., he has no idea what he is trying to describe. It's childish and unrealistic.
All I can say about "Flowers for Algernon" the short story — I was thinking that the novel must be much better for this to be considered worthwhile. But then there is an addendum at the end of this:
> The novel, published as a mainstream work by Harcourt Brace Jovanovich, is not as effective as the story version, which is much tighter and written from a very successfully executed first-person point of view.
Soo… yeah. I'm not gonna try it right now. But then, again, I must admit that anybody who mostly likes sci-fi shouldn't even listen to me, because I can say only bad things about vast majority of famous sci-fi books, with only just a couple exceptions. Mostly it's literally just pulp fiction, comic books without pictures. Not what I expect when somebody talks about "literature".