As a PhD applicant who visited at an Open Day and has some links to the uni, here are my conclusions so far:
It's good but not absolutely amazing for undergraduate studies. It's got one of the best medical schools in the UK and the best Dentistry department. Materials engineering is also very good there. The rest of the courses are definitely good, but probably not on par with UCL/Imperial.
However...
On the postgraduate and research side of things, it's one of the best universities in the UK (hovering around the 10th place, currently 11th as ranked by the RAE). It prides itself in having put out several Nobel Laureates, while the top 10 uni. I'm currently at can't say the same. It's got the highest research budget of any university not in the Russell Group.
It outranks Durham, St. Andrews, Bath, KCL, Nottingham, RHUL and a lot of others that are otherwise considered top unis.
The only reason why QMUL ranks so low in the rankings is because of its lenient undergrad entry requirements (one of the main league table criteria), something that the University wants, simply because it was founded on the original People's Palace principles of giving people a chance at 'high class' life (the conditions in the East End were a lot worse in the 1800's). Even so, QMUL hovers around the 20-40 mark in overall league tables which is NOT bad by any stretch of the imagination. If you want to do a top class undergrad course, I guess you're better off trying UCL or Imperial (or maybe something like York or Bath), but it's not bad as a second choice.
The campus looks great and very friendly, although I think I will miss my current uni. a lot, and I really hope I can come back one day in some regard. QMUL doesn't have forests and lakes and other stuff like that, it's a lot more urban and modern, but that also means you don't get to live in fetid 50's (or older) buildings for your accomodation.
The only thing that put me off slightly at the Open Day was that pretty much everyone there was (way) older than me, and I couldn't find anyone to socialize with, but then again it was a postgrad day. It's VERY multicultural, which is not a bad thing at all, but I can imagine feeling a bit distant due to culture shock. I'm sure I'll find friends if I end up going there, but I'll probably keep traveling back here once in a while to keep attending society meetings and other things.