I enjoyed this quite a bit, though there is a lot more sex involved than in what I normally read.
I've been on a huge mythology kick lately (thanks Percy Jackson!), and this fit the bill for me, though clearly in a different way. I liked the characters, and once I got past the sheer cheesiness of the premise (let's be honest, it's a bit cheesy and fanfic-y, and I love fanfic), I was quite hooked. There was a bit of a mystery, a decent chunk of action, a romance that turned out sweeter than I expected, and lots of history.
I loved all the history. I'm a history nerd, and I'm proud of it, and ancient history in particular is fascinating to me. Having Julian thinking back on his life was fascinating reading (in between all the smut...), and I liked that it didn't read like a history book of the time period: Julian had his own views on the Romans and on what was going on at the time.
It was also funny. Not laugh-riot funny, but I was smiling at quite a few of the lines and really enjoying the writing. Julian and Grace were both amusing and snarky and a little exasperated with the strange situation they found themselves in, and they weren't afraid to say so.
I'm glad I read this, and I'll definitely be going through the rest of the series. I love mythology and humor together; it's my secret (not so secret now, I guess) weakness, and this worked for me.