Literature Not a terrible series, but it could use some work
Now, I'll admit I'm a huge Riordan fan. His books have been extremely interesting and taught me more about greek mythology than any history class could. But really, it could use some work. It's not that it's terrible, per say, it's just that it's mediocre by book standards. Especially conpared to Rioedans later works, especially Magnus Chase and Trials of Apollo (controversy over LGBT+ issues Notwithstanding).
It has a lot of, shall we say, issues when it comes to characters. While Annabeth certainly has her time to shine in future books, here she pretty much serves as exposition despite the fact that she sould be able to connect the dots in traps, The theme park trap in the first book being a good example. And while Grover's a pretty funny and likable guy, he doesn't really do much. Percy, more or less, does almost everything. And, honestly, it's a little disconcerting when you aknowledge how stupid he can be sometimes. He definitely grows as a character more and steps put of the "does everything" role as the franchise progresses, but he does it a lot early on.
Alltogether, it isn't a terrible book, and is in fact very enjoyable, but it definitely isn't Riordan's best work. Still, I suggest you to read it as if you ignore these issues it is a fun book.
Literature A good series
I've always loved the books so I may sound a bit fanboyish, but I'll try.
What really makes them good is the strong plot's and interesting use of mythology. The dialog can seem a bit corny here and there, but usually it can add some good humor, and for the most part the characters are interesting.
Another plus is the ability to make villains sympathetic and the good use of foreshadowing, though I admit the final battle seemed rather lacking, it's easy to overlook. The 3rd book is personally my favorite and the 2nd book my least favorite.
Overall, it has it's flaws, but certainly worth a look.