MetaTrader is good and fairly reliable as an automated trading platform. It also provides free access to historic data and the backtesting tools are adequate for most types of strategies. I've found it to be considerably better than tools like OpenQuant which costs far more.
The downside is that typically you can only use it for Forex (and some CFD's) and typically only with low-end brokers that tend to have quite high transaction costs. It's a cheap way to get started but it's no good for high frequency or large volume.