Personally, I found both Artimis fowl and the percy jackson books felt a little too safe and kiddy to me. They were fun, but I never really got the sence that anything seriously bad might happen to a given character, hell in Percy Jackson the monsters don't even die, much less have actual battles, they just get zapped and teleported away.
This is why I only read up to Percy Jackson and the last olympian and wy I likely won't be reading any more of the series, since even a ya series I prefer to feel that characters aren't safe and bad things might happen, and hell yes the final ending might be bad, hell look at the death count in harry potter or the bloody grim ending of the Hungar games as examples of ya fiction with that sense of darkness.
On the topic of endings generally, on the one hand I do find it depressing how common pop corn, happily every after endings are. On the other, if the happy ending has been earned with enough bad stuff happening, or has enough of a sting in the tale, then they can work quite well, indeed following George R R Martin there is almost these days an anti happy policy, which has just as many pit falls as the alternative \if the grim ending feels just like a cop out.
to take one example, China Mievil is someone I don't think does! happy endings, howeever where I appreciated the ending to Perdido street station and to Iron council, I was less keen on the ending of The Scar, mostly because the main character was a really cold, unemotional scumbag who was largely unaffected by anything so you really didn't care where she ended up, and the nicest character in the book who'd been through the ringer was just left hanging following a tragedy and you weren't sure what happened to him.
It also depends as Bookrage said upon genre and style, for example horror, cyberpunk and distopea often have very grim endings, indeed a favourite of mine that falls into all three of those categories is Harlen Ellison's classic novella I have no mouth but i must scream.
On the other hand, sometimes when your expecting! a super grim ending and something good happens, if the author has shown themselves capable of being grim and killing people it can actually have the opposite effect, for example Rand was so bound to die at the end of the wheel of time was quite the surprise that he didn't.
Then of course, with multiple characters, you can have it happy for some and not for others, this indeed seems the tendency in many series.
I personally think this is song of ice and fire will go, although I will say from the other fiction I've read by martin he isn't exactly a man to do happy endings, still I'd rather like it if he did let some characters such as daenerys come to a place of piece eventually.
With our dreaming and singing, Ceaseless and sorrowless we! The glory about us clinging Of the glorious futures we see,
Our souls with high music ringing; O men! It must ever be
That we dwell in our dreaming and singing, A little apart from ye. (Arthur O'Shaughnessy 1873.)