I worked there for four years before leaving for the City.
* When I was there, there was an extremely hierarchical management structure, which was inefficient. I didn't get an 'initial' three-month review for over a year, and if I wanted to communicate something to management, it had to go all the way up the chain and down again.
* They don't offer great opportunities for development and growth.
* They almost never sack people, which might sound like a good thing, but I came to learn is actually a red flag for a company. It meant that the better / more personable coders tended to move on, while the people who wouldn't get a job elsewhere stayed on.
* Salary is opaque and not competitive... beware (at least when I was there) the figure quoted to graduates is a "total package", which includes e.g. value of healthcare, employer contributions to pension, etc. Clarify the actual salary before accepting the offer, and sadly, take any assurances about profit share or future salary growth with a lorryful of salt.
Ultimately the reasons that I left were the uncompetitive salary, the lack of opportunities for development, and the sense that MetaSwitch was stagnating.
However, there is a strong company culture, and I met some great people there (though it has to be said, they have all now also left...).