Mine's going to be a rehash of some already selected. A few are older than 3 years.
Away We Go
I'll 2nd, 3rd, 4th, whatever we're up to-- John Carter. It's not the greatest movie, by any stretch, but like others have mentioned, the ad campaign and the internet backlash of the movie were the downfall. It's really not as bad as it's made out to be. I was pleasantly surprised in that it was an enjoyable sci-fi movie.
Going back a few years more (both from 2004)--Miracle and Eternal Sunshine of the Spotless Mind.
Drag Me to Hell - Old school Sam Raimi movie made in 2009. Better than the more hyped Insidious.
Drag Me to Hell got soooooo hyped over here, way more than Insidious which didn't seem to get any attention. To be honest I thought they both sucked but I disliked Drag Me to Hell more because of how much hype it got
I don't know what people on here think of Cabin in the Woods but everyone I know seems to dislike it, so I'll put that up as an under-rated favourite of mine, I thought it was great.
Seen a few people mention The Amazing Spider-Man. I thought it was great at the cinema, but then on blu-ray I didn't really enjoy it for some reason. I noticed a lot more product placement on the blu-ray and got a bit distracted by it. I'll have to watch it again some time though and I am looking forward to see what they do in the sequel.