I think TechniSol had summarized it very well: from an hardware point of view, Kobo's devices in general are good, but not perfectly refined (e.g. the micro usb slot has no door).
Problems are mostly with software: from a firmware to another, we gain and lost at the same time. This is not crucial (the chess game is not working since 2.4), but just annoying (e.g. long paragraphs that split the screen erratically).
For one important thing, Kobo is really lucky: to have a very good community here, trying to help, pointing out not only problems, but also solutions.
I don't hate Kobo, but generally I like people using it more.