I started Armed & Magical immediately after finishing Magic Lost, Trouble Found, and it was a good decision. Armed & Magical picks up right where the first book ends. Raine is still burdened with the Saghred, which continually flexes its psychic muscle. Sarad Nukpana lurks on the edge of her awareness. There's elves and goblins after her, not to mention any number of mages who might want her power for their own.
I love how Raine explains the Saghred, calling it her "psychic roommate." Lisa Shearin's easygoing, matter-of-fact characterization of Raine makes the book extremely fun. If you enjoyed Magic Lost, Trouble Found, then you will enjoy this book. If you didn't, then I don't see why you'd be reading the second one just to see if it "gets better." The plot certainly thickens, but it follows the same general formula that the first book did, incorporating some new twists to keep it interesting.
If you haven't read Magic Lost, Trouble Found first, don't even think about skipping it and reading this one. You probably won't get lost. Shearin does a good job adding exposition that catches readers up to Raine's life, some of which is targeted at people who may not have read the first book (or read the first book long enough ago to forget it). Actually, this is something with which I have an issue: reading the books back to back, I noticed that some of those snippets were reused verbatim from the first book. While I suppose that it's hard to improve on nice, tight prose, what's the harm in trying?
I liked the ending to this book much better than the first one. The climax was paced better, wasn't too drawn out, and the ending wrapped up enough loose ends while still leaving me hungry for book 3.
I guess the highest praise I could give this book would be: I read it as quickly as possible because I couldn't wait to find out what happened next, so quickly that sometimes I had to go back to double check something.