I can say as a foreigner who's been living in London for the last 8 years (with 1 year break for Essex coast) that yes, it's possible to get tired of London, without being tired of life. And no, it's not like every foreigner likes London, it's just that either natives aren't really interested or some foreigners are afraid to say what they think.
It's just like any big city with its problems. I can honestly say that it is the best city in Europe to visit as a tourist (comparing with Rome, Paris, Warsaw, Madrid, Berlin, Vienna). Amazing things to see, convenient to travel on weekends and surprisingly cheap if one knows where to go. Some parks are great - especially Richmond, but Bushy or Greenwich are also great. Restaurants are great.
But for me it's awful to live in every day, especially living in Lewisham (recently mentioned on BBC as the most dangerous borough in the UK). It's crowded, driving anywhere is a pain, dirty, there's a big mess with social housing spread among other buildings and immigrants not integrating with the locals (and that's coming from an immigrant), everyone is trying to get to the lowest possible denominator. Every business just MUST be located in the centre, like there wasn't a huge open space around M25. As a result morning and after commute are a pain when thousands of people needlessly have to get to the same place and get out from the same place.
Some people will love it. Some of my friends do, especially those that prefer restaurants and theatres to open, wild places. For me it's a pain. But just 2 more months;-)