The answer I use is "I love this kind of work and I'm really looking forward to applying my skills to a new challenge". It's an enthusiastic tone that reassures competence by bringing up your skills and hits two of the big HR type buzzwords "forward" and "challenge".
Yeah, also I would add something like " and leaving my old work has had its benefits as it has given me a chance to look at other perhaps more promising avenues"
Because he won't assume Malc just needs another job to pay bills and is committed
Yeah, I usually answer that the technical aspects are interesting, appeal to me as an area I want to grow in and I enjoy a challenge. Got laid off so no need to elaborate on why I left it