I don't know if I could call it the "most boring", but near to the top of the list for me is Shadow of the Colossus. Now, I love the idea of the game, and I don't want anyone to take my inclusion of it here as me saying it is bad. It isn't, it is good. It just requires patience, at least at the beginning. After you've made you first kill you're sent off to slay another, all the while without much hint as to where exactly you're supposed to go. The map is huge and you have access to a lot of it, which I feel to be part of the problem, actually it is probably my biggest hurdle with the game. Perhaps my familiarity with the Zelda series was my downfall here, as in those games you are blocked off from places you can't go until you're supposed to go there. There's a block you need to bomb, or you need the grapple hook.
SotC doesn't really have that, instead you are mostly left to wander which, again I like the idea of, but in action it slows things down. Well, this coupled with the technical limitations that are trying a bit too hard to render a big world. (I assume this is better on the new HD remix, but I'm going off the PS2 version I have sitting on my shelf.) I also don't like using guides on games I haven't beaten and I'm the only one of my close circle of friends who has even played the game. Essentially, I'm (of my own will) alone in a big world that I really, really want to explore and like but can't attain the free time needed to get hooked. It is far from bad, and has a great idea, but to fit the topic at hand- it is boring.
---In addition---
The above is an example of a good game that is tough to get into therefore boring. I don't intend to go into the list of games that are boring because they are bad and therefore entirely not fun to play. As well, I tend to find First person shooters (at lease online focused ones), as well as realistic racers boring simply because they are not my genre. In both of those I'd rather play a "futuristic" version of them than the normal. (example: when it comes to racing I'll take F-Zero or a Kart racer over real cars on real tracks)
