The best thing about Holga cameras is that their weaknesses are their strengths; they don't auto-advance the next frame once the picture is taken, but they don't lock the shutter button, either. Also, depending on the speed of film used, along with the 1/100sec shutter speed, it's possible to do multiple exposures without risking a wash-out, opening up the possibilities of double, triple, even quadruple and beyond exposures. Sadly, this composition doesn't take advantage of these possibilities, or even stand well as a traditional double-exposure.

Essentially, we've got two images, which we'll refer to as "The Building" (the obvious one and, from the looks of it, the first exposure) and "The Abstract" (to its credit, I'm completely stumped as to what it is, that deserves recognition), but there doesn't seem to be much to the overlap. Granted, there's no strict guideline in multiple exposure for how the two images should or should not relate, but the relationship between The Building and The Abstract is so indecipherable, that it's far too easy to dismiss it as a mistake on the part of the photographer. Serendipity is no bad thing, mind you, but the "serene" part is just not here; it's noisy and messy. Perhaps if The Building had been better composed in the frame, such as moved closer (since we know Holgas don't have zooms) or moved up so the foreground grass doesn't conflict with The Abstract, there might have been something more visually compelling here, but as it is now, it really does just look like an accident.

What I'd like to see in the future, based on what it looks like you were trying to do here, is matte-work instead of just multiple exposures. The Abstract would be great if it were "matted" into the skyline using two pieces of black card, one in the sihlouette (or approximation) of The Building, and the other of the skyline. That way, the abstract would become the sky. Double/multiple exposures is a pretty well-worn path, with staples like "ghosts" or "two setting suns", but matte-work seems unexplored, as if monopolized by the film industry.

The presence of The Abstract shows a skill you have as a photographer I admire wholeheartedly: the ability to use a camera, a device designed to replicate reality, to create something abstract. It's not an easy thing to do, and you seem to be moving along the right path. Now, you just need to take that to the next level, and it's easy to see the potential you'd have for that by looking at this photo.

So, to close, you've tapped into a great resource the camera has to offer (You've also made me miss my Holga), you've shown an eye for both the abstract and the concrete in photography (a rare skill), now you have to kick it up a notch. My advice would be to invest in some black construction paper or posterboard and experiment with some matte-work, but that's just me. Otherwise, this is a very good start, but it's only a start. As harsh as I've been, the fact is I do like this image a little more each time I see it, so just imagine what your next could do.