The Renault Mégane II made an impression with its bold design (abrupt tailgate) and unprecedented level of passive safety (first compact car with 5 EuroNCAP stars). Voted Car of the Year 2003, it achieved immense commercial success. However, its career is split into two: a Phase 1 (2002-2005) notoriously known for its catastrophic breakdowns (faltering electronics, turbo failures on diesels, injection), and a Phase 2 (2006-2009) largely made more reliable. As an expert, the analysis of this model requires a strict separation between these two periods, particularly for the diesel (dCi) engines which concentrate the majority of serious failures.
The Renault Mégane II is a textbook example of a two-faced car. Absolutely avoid Phase 1 diesel models (2002-2005), especially the 1.9 dCi 120hp and 1.5 dCi (80/100hp), whose failures can cost more than the car's value. However, Phase 2 (from 2006 onwards) is an excellent used car deal. The 1.5 dCi 105hp and 1.9 dCi 130hp have been corrected, and the chain-driven 2.0 dCi 150hp is a model of reliability. Gasoline versions are generally trouble-free, with the exception of ignition coils. Buy a Phase 2 with a clear history, and you'll have a comfortable, safe, and very affordable compact car.