In this paper a systematic evaluation is presented of an e-participation platform based on GIS tools. The evaluation methodology is founded on the Technology Acceptance Model (TAM), which has been elaborated and adapted to this particular type of IS, taking into account the particular objectives and capabilities of this platform. Our main evaluation dimensions were usage, ease of use, functional usefulness, political usefulness and importance of discussion topic; each of them has been analyzed into a number of sub-dimensions. Using this methodology five pilot applications of this platform in 'real-life' situations and problems have been evaluated with both quantitative and qualitative techniques. Finally it has been concluded that the use of GIS tools can provide significant value in the area of e-participation, which however depends on a number of context factors, such as citizens' computer literacy and familiarization, trust to the political system, interest of the sponsoring public authorities, appropriate promotion, importance of the topic under discussion and quantity and quality of reference information appended on the digital maps by public authorities.