Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Good concept, poor execution

When roomba works it is great, but based on my experience and many comments available on the internet it is trouble-plagued. Roomba has a three month warranty with parts being replaced up to six months. For troubles during the warranty period, they replace parts, including roomba itself, readily although you still have to pay shipping charges, about $20, if they replace the unit. However, after the warranty period, if something goes wrong you have had it. ROOMBA CANNOT BE REPAIRED. Unfortunately, things frequently do go wrong.I think that most of the good ratings of roomba, even by publications, are made after initial use before the troubles show up. I am amazed that the company has done nothing to improve quality or, at least, made the unit repairable. After about nine months I now own an unrepairable, i.e. worthless, roomba.