I mentioned, earlier, that I was reading The Son of Neptune during the last Caps game.
I never got around to writing up much of a review on its predecessor in the series, and nothing at all that made it out of my notes. To sum up my thoughts, I liked the three main characters quite a bit and I liked the idea as well.
What I found interesting was contrasting the Greek gods versus the Roman ones, because I'd always thought of them as interchangeable. I still haven't gone back to any of my greek mythology books, to see whether that perception of mine was due to the books I read, or my misreading of those books, or whether Riordan just made up those differences.
One thing that struck me about the Percy Jackson books is that most of them comprise a mostly-identical retelling of the labors of Hercules. It didn't jump out at me that that was being done in the first book (nor in the second, come to that), but I suspect that the rest of the series will end up being much the same as Jason and the Argonauts. I should really re-read that legend before starting on the third book. (And I originally saw Jason as being in charge of the Argo II, but this one made me wonder if that will, indeed, be the case. Thinking about it, wasn't Hercules part of the crew of the original? Something to think on.)
So, what was good about Son of Neptune? Again, the three main characters are quite compelling. They each have their strengths and weaknesses (although Frank's stated clumsiness is never backed up by clumsy action, it occurs to me now), and they make a good team.
The Roman camp is interesting, and mostly well done. Them having an aqueduct didn't make much sense, given the lake right there, but that was a fairly minor thing. The camp part of it was good, as that fit well with Roman legions.
I also liked that the 'son of Neptune' who would take away Hazel's curse is actually a horse. That was very cute, and well done.
What didn't I like? There were a couple of minor consistency issues (three times I felt like there was a reference back to something that hadn't actually been mentioned, although I didn't check any of the three). There might have been another, more significant one, too, now that I think about it. I believe it was all giants that could only be killed by a god and a demigod working together, and that was only true of one of the two, here (although that one was really funny). SPQR showed up (inevitably) in both books, with slightly different spellings in each (the SPQ part was the same in both, Senatus PopulusQue, which is correct. But the R was Romani in the first and Romanus in the second. The fact that they are different is interesting, but the correct is Romanorum, so both are wrong. The fact that I know that tells you that I saw part of what was going on very early on in the first book). Also, the idea that people would set out to accomplish something with no prospect of being able to finish it kind of bugged me (they had an ill-defined goal taking place somewhere in an area of several million square miles with no way to get there or back). And they didn't seem especially concerned about this prospect (the large area part of it was shown, later, that they knew that, but if they did, they should have showed that concern much more readily at the beginning. So showing it came out as... less than genuine, I guess).
Expanding on that idea, Mars "prophecy" that set them on their quest was done in a way that I found very funny, but it didn't make a whole lot of sense. Him giving them something to go on, some way to make the quest seem possible, would have been a lot better.
The last thing I don't think I liked is that the victory at the end of the second book is too complete, too pat. I'm not sure why that bothers me, as it generally doesn't, but I think it's mostly that I expected more in the way of sacrifice. There was too much talk of that being important, and too little of it actually happening.
But I definitely enjoyed both books, and am even tempted to re-read them (perhaps along with the Percy Jackson series) to see how things tie together (mostly, to see if there are some things I missed, as I expect that there are).