My experience with Holga cameras started with the 120N model, which is the medium format film equivalent of this camera. I absolutely love the 120N; I take it everywhere along with my digital camera and tend to get my best photos with it. I decided a year ago to try out the Holga 135. After many rolls shot, developed, and processed by me, it has consistently failed to live up to expectations.
The main problem with this camera is it's lens is too narrow. The classic Holga 120 has a fairly wide angle lens, but the narrow 135 captures only a fraction of a person's view compared to the 120 model. For this type of camera, which has almost no settings to begin with, a wide angle lens is more desirable- it's easier to either take a few steps forward or just crop the final image with a wider lens than having to take 50 steps back to try to cram all your surroundings within the narrow frame. There is a Holga Wide Angle Lens Adapter that you can buy and attach to the 135, but it causes too much distortion for my tastes.
The other issue is the 35mm film. The 120N takes medium format film, which has about 4-5 times the surface area as 35mm. So even though the lens is plastic, because the negatives are so huge, most photos (properly focused) come out very sharp and crisp in the center of the frame with the classic vignetting and blur toward the edges. The 135 produces much smaller 35mm negatives. As a result, pretty much all the photos look pretty dull from edge to edge, lacking any sort of crispness whatsoever. Because of how the 135 is designed, there is no natural vignetting and no light leaks (if you're into that).
If you're considering trying out a Holga, I'd highly recommend the 120 model. If the size and scarcity of the film intimidates you, rest assured that it is really easy to learn how to develop black and white film yourself in your own bathroom, or you can just drop the rolls off at Walmart and get back prints in 2 weeks. The 120 and the 135 are completely different cameras, and the 35mm version unfortunately does not produce any of the desirable "Holga-ness" that you may expect.