My thoughts on MHI:
It's two buckets of fun with a dash of yippee. It's a very good debut, and I enjoyed it a lot. It is a little overlong, and the battle in the swamp is so climactic that it almost overshadows the end, but it's a whale of a good time, and I'm looking forward to the sequel(s).
The action sequences range from very good to flat-out terrific. My favorite is the gargoyle assault on the asylum: the first glimpse of the gargoyles is nicely hair-raising, and the way the action unfolds from there is just wonderful. Many points for the car chase, and for the dude in the NRA hat who finally had an opportunity to use his boat anchor. My least favorite: possibly the battle in the swamp, not because it was ineffective, but because I couldn't believe you were killing so many of the cast with so much book to go -- and then they all died and came back, and I went, "meh." That could come back to bite you. if you do kill any of 'em in the future, it could come off as anti-climactic: we've seen them die; we've suffered that loss.
The writing is very strong in general -- the humorous asides are especially well done -- and you did a great job making me like the team: my favorite was Holly, but Trip was terrific, as were Skippy, Gretchen and company. Nice job of creating an interesting mix of different characters: you manage to make the team pleasantly diverse while spoofing the tendency toward PC-ness, and it works out pretty well. The downside, if there is one, is that they come together almost too smoothly: the only person who's really different from that is Grant, and that's because of his attitude, not because of his outlook. But it makes for a fun time and a good team.
A word on Grant: my favorite part involving him is the humanizing little scene he gets, when Owen's eavesdropping reveals that Grant is upset to be beaten at anything, to make a bad call, because if he's anything less than perfect he's not good enough. It's hard to make anybody feel bad for the Golden Boy, but you did a great job of making Grant a character there, as somebody Julie could believably fall for; the rest of the time, he's Stock Jerk Boyfriend #437, not really a person. (I like Julie's Evil!Vampire!Mom for that reason: she's not just the evil vampire figure, she's an evil vampire who is horrifyingly mothering, and that breaks her out of stock mold. Grant could have used more humanizing.)
My biggest problem with the story was Julie. She didn't really give me a strong sense of her as a character for a long while, and that meant that the love story was the weakest part of MHI for me. Julie appears as pretty much the ideal woman for a lot of gun nuts: she's beautiful and loves guns, whoopee! ...but I didn't get a sense of why Owen fell for her beyond that. Yeah, lust, I can believe immediately, even a crush, but growing love? That was a bit weak from my point of view. More importantly, I didn't get a sense of why she'd fall for him. For the early part of MHI, Owen comes off as the guy with a crush on her, and a disturbing hatred of her boyfriend. This does a great job of dramatizing the darker side of Owen, the things about himself that he represses and is afraid of, but it doesn't do very well at making Owen seem like a logical choice for Julie. When, early on, she told him she understood how he felt, I was surprised that she gave him that much of a window rather than crush his hopes.
Oh, and you forgot my patch.
But it's definitely a fun book, and it does a great job of cheerful gun fun without being didactic -- a major problem with a lot of the books catering to our demographic.