During the year that I worked in London (while living in Winchester) I saw this pub every day as I exited Waterloo station to walk up to Clerkenwell. It was one of those "I must pop in there some time to see how it is, perhaps next time there is a big delay with the trains on my way home." In the end, I didn't end up going there until the day before my last day at my London job. I had just given a particularly ravishing colleague of mine a guided tour of how to walk from our workplace to Waterloo. As a reward, she suggested going for a drink, so I thought, "Hey, why not the Hole in the Wall."
I'll concur with RichLightWeight about the ambience and quality of this place. It leaves much to be desired. My ravishing colleague bought us each a pint of my choice. I chose the Battersea Bitter, which was not "in good nick" then either. Despite the average-to-below-average quality of the beer and the ambience, I didn't dwell on it too much because I was busy conversing with the aforementioned ravishing colleague. Then it was time to catch the next train, so we ducked out of their, going our separate ways.
So, yeah, to sum up: this place is not a bad bet for a quick couple of pints if you're stuck waiting for a train or if you've been offered a drink by a ravishing colleague after having just arrived at Waterloo together, but don't make it a destination in and of itself because you'll be quite disappointed. "Hole in the Wall" is an apt name to call this joint.
Very small bar in the front so we headed into the back. On cask, I tried the Adnams, a nice twickenham ale, and a tasty offering from Battersea. I found all ales to be in good condition. Atmosphere is funky, they do have a bunch of Shepeards Neame posters as apparently they have this on cask... It was off when we visited and the bartender turned us on to the Twickenham and battersea. Thus the good service rating. Food was average at best. What was amazing was that being under a railway arch, every time a train went over the whole place shook! I'd check it out if you're in the area, and if you don't see anything interesting move along as there are a lot of interesting places within a 15-20 minute walk.