Yep, the STM is a bit restrictive as I've hit it a few times without realising how much I'd downloaded. They could do with increasing the limit a bit, cause 3GB between 4pm and 9pm is very easily achieved these days.
Their customer service is appalling. Never known any company like it. However, if they get everything right first time and you don't need to call them then you'll be OK.
I'm on the 20MB line, and it is very good - fast and reliable. What more could you ask for? It's not cheap compared to the LLU ADSL offerings, but you do get what you pay for. For gamers, it's a no-brainer, imo.