It's fun working with something brand new. In this case it's fun photographing with the 19mm and 30mm Sigmas. New equipment opens up new opportunities for creative expression, or at least that's the official line.
Everything you expect a new lens to produce has been preconditioned by all the other lenses you've ever used. And no matter how much you promise yourself you'll never be surprised with your next purchase, every new lens will surprise you. Such is the case with the Sigmas.
They surprise me because of the kinds of interesting and quality images I'm pulling from them with the NEX-5N, different from the lenses I get from all my Pens and µ4:3rds lenses. Not better, different. I had no idea what I'd get from these two on the 5N. So far I've used the Sony 18-55mm kit zoom primarily, with a smattering of the OM 28mm and 50mm using a Fotodiox adapter. The same thing is happening to a lesser extent with the µ4:3rds Olympus E-M5, but that's with a new body and existing lenses. It's not quite the same.
The more I use these Sigma lenses with the 5N, the more interesting they become. You may not like the photographs I produce with them, but I certainly do. They're different in a good way, and I like different. This does not mean I'm abandoning µ4:3rds. But I'll never be totally depend on it again the way I totally depended on regular 4:3rds. Or Olympus. I'll never depend on any one manufacturer again unless I absolutely have to.