I took the risk last year with one of my mates because our original plan fell through at the last possible minute after arriving in Clapham, and we didn't really fancy hanging in a no-doubt packed bar just the two of us, so throwing caution to the wind we hopped on a train to Central. In hindsight, we wouldn't have got home any earlier anyway had our original plan worked out because trains out of Waterloo stopped running at like 10pm (the station was being slowly closed off, zombie-apocalypse style, when we got there just after 9pm).
When we got along the South Bank, by the Eye, although it was busy, we could have easily kept a really good viewing spot. We were literally behind where the fireworks were eventually deployed. But in our infinite wisdom, and because I sure as fuck wasn't standing around in the cold for a little under 3 hours, we decided to walk alllllllll the way along the river, over Black Friars, and down the Victoria Embankment. That was when we regretted our decision. Near Embankment station, which was closed this time last year, there was a road block, and the crowd had come to a standstill. We turned around and headed back toward Black Friars, but the sheer volume of people was otherworldly - I had never seen or experienced anything like it. After much faffing around, and dismissing the idea of walking back to Clapham(!), we settled at the north end of Black Friars with not such a bad view of the Eye. We watched the fireworks...then came our 4 hour slog home.
It was absolute hell, but I'm sort of glad we did it because I got to see the fireworks, live, in our country's capital on New Year's Eve.
Buuuuuut don't do it, if only out of principal because they've decided to start charging for tickets for the first time ever.